Semiconductor device

ABSTRACT

A flexible area  2  is joined at one end via a thermal insulation area  7  to a semiconductor substrate  3  which becomes a frame and at an opposite end to a moving element  5 . The thermal insulation area  7  is made of a thermal insulation material a resin such as polyimide or a fluoridated resin. The flexible area  2  is made up of a thin portion  2 S and a thin film  2 M different in thermal expansion coefficient. When a diffused resistor  6  formed on the surface of the thin portion  2 S is heated, the flexible area  2  is displaced because of the thermal expansion difference between the thin portion  2 S and the thin film  2 M, and the moving element  5  is displayed with respect to the semiconductor substrate  3.

This is a Division of application Ser. No. 09/511,948, filed Feb. 23,2000, now U.S. Pat. No. 6,384,509.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates to a semiconductor device made up of asemiconductor substrate, a flexible area isolated from the semiconductorsubstrate and displaced in response to temperature change, and a heatinsulation area placed between the semiconductor substrate and theflexible area, a semiconductor microactuator using the semiconductordevice, a semiconductor microvalve, a semiconductor microrelay, and asemiconductor microactuator manufacturing method.

2. Related Art

A semiconductor microactuator includes at least two materials havingdifferent thermal expansion coefficients in combination as a bimetalstructure wherein the bimetal structure is heated and the differencebetween the thermal expansion coefficients is used to providedisplacement is available as a mechanism using a semiconductor devicemade up of a semiconductor substrate, a flexible area isolated from thesemiconductor substrate and displaced in response to temperature change,and a heat insulation area placed between the semiconductor substrateand the flexible area. The semiconductor microactuator is disclosed inU.S. Pat. No. 5,069,419 “Semiconductor microactuator.”

A semiconductor microactuator described in U.S. Pat. No. 5,069,419 is asshown in FIG. 53 (top view) and FIG. 54 (sectional view); it has aflexible area of a bimetal structure comprising an aluminum thin film304 formed in a part of a silicon diaphragm 300. If an electric currentis made to flow into a heater 301 formed in the silicon diaphragm 300,heat is generated and the temperature of the diaphragm 300 rises. Sincesilicon and aluminum differ largely in thermal expansion coefficient, athermal stress occurs, bending the diaphragm 300, producing displacementof a moving part 305 placed contiguous with the diaphragm 300. Toprovide efficient displacement, a hinge 303 of a silicon dioxide thinfilm is placed between the periphery of the diaphragm 300 and a siliconframe 302 of a semiconductor substrate for preventing heat generated inthe diaphragm 300 from escaping to the silicon frame 302.

However, considering the current state of application, it is desired tofurthermore decrease the heat loss. Specifically, the heat escape (heatloss) is thought of as power (consumption power) supplied all the timeto maintain the diaphragm 300 at a predetermined temperature (forexample, 150° C.).

Then, it is desired that the power consumption is 100 mW or lessconsidering miniature, portable battery-driven applications.

Further, as examples of semiconductor microrelays in related arts,semiconductor microrelays are disclosed in JP-A-6-338244 andJP-A-7-14483. The semiconductor microrelays disclosed therein will bediscussed with reference to the accompanying drawing.

FIG. 55 is a sectional view to show the structure of the semiconductormicrorelay in the related art. As shown in FIG. 55, the semiconductormicrorelay has a cantilever beam 313 having a first thermal expansioncoefficient and made of a silicon monocrystalline substrate 312 with anopposite end supported so that one end can be moved. On the rear side ofthe cantilever beam 313, the semiconductor microrelay has a metal layer315 having a second thermal expansion coefficient larger than the firstthermal expansion coefficient via a conductive layer 315. On the mainsurface of the cantilever beam 313, a contact circuit 317 is providedvia an oxide film 314 on the one end side. Also, a heater circuit 318 isprovided via the oxide film 314 on the roughly full face of the mainsurface of the cantilever beam 313.

On the other hand, an opposed contact part 320 having a conductive layer319 as an opposed surface is provided at a position facing the contractcircuit 317 with a predetermined space above the contract circuit 317.An electric current is made to flow into the heater circuit 318, wherebythe heater circuit 318 is heated. Thus, a flexible area consisting ofthe cantilever beam 313 and the metal layer 316 is heated. At this time,the thermal expansion coefficient of the metal layer 316 is set largerthan that of the cantilever beam 313, so that the cantilever beam 313and the metal layer 316 are displaced upward. Therefore, the contactcircuit 317 provided on the one end of the cantilever beam 313 ispressed against the opposed contact part 320 and is brought intoconduction. Such a bimetal-driven relay enables an increase in thecontact spacing and an increase in the contact load as compared with aconventional electrostatically driven relay. Thus, a relay with smallcontact resistance and good reliability with less welds, etc., can beprovided.

However, the semiconductor microrelay in the related art also involvesthe following problem: To drive the relay, it is necessary to make anelectric current flow into the heater circuit 318 provided on the mainsurface of the cantilever beam 313 for heating the cantilever beam 313and the metal layer 316. However, the silicon monocrystal forming thecantilever beam 313 is a material having very good thermal conductivity,the cantilever beam 313 is connected at the opposite end to the siliconmonocrystalline substrate 312, and large heat is escaped from thecantilever beam 313 to the silicon monocrystalline substrate 312, sothat it becomes extremely difficult to raise the temperature of thecantilever beam 313 with small power consumption.

That is, with the semiconductor microrelay in the related art, largepower must be supplied all the time to maintain the conduction state.The value is extremely large as compared with a mechanical relay thatcan be driven with several ten mW. For practical use, realizing lowpower consumption is a large challenge.

SUMMARY OF INVENTION

As described above, the semiconductor microactuator using thesemiconductor device, the semiconductor microvalve, and thesemiconductor microrelay in the related arts require large powerconsumption and thus it becomes difficult to drive them with a batteryand it is made impossible to miniaturize them for portable use.

It is therefore an object of the invention to provide a semiconductordevice with small power consumption, manufactured by an easymanufacturing process, a semiconductor microactuator using thesemiconductor device, a semiconductor microvalve, a semiconductormicrorelay, and a semiconductor microactuator manufacturing method.

To the end, according to a first aspect of the present invention, thereis provided a semiconductor device comprising a semiconductor substrate,a flexible area being isolated from the semiconductor substrate anddisplaced in response to temperature change, and a thermal insulationarea being placed between the semiconductor substrate and the flexiblearea and made of a resin for joining the semiconductor substrate and theflexible area. The thermal insulation area made of a resin is placedbetween the semiconductor substrate and the flexible area, whereby heatescape when the temperature of the flexible area is changed isprevented, so that power consumption can be suppressed and further themanufacturing method is simple.

In a second aspect to the present invention, in the semiconductor deviceas first aspect of the present invention, the material of which thethermal insulation area is made has a thermal conductivity coefficientof about 0.4 W/(m° C.) or less. The heat insulation properties betweenthe flexible area and the semiconductor substrate are enhanced.

In a third aspect of the present invention, in the semiconductor deviceas the second aspect of the present invention, the material of which thethermal insulation area is made is polyimide. The heat insulationproperties between the flexible area and the semiconductor substrate areenhanced and manufacturing the semiconductor device is facilitated.

In a fourth aspect of the present invention, in the third aspect of thepresent invention, the material of which the thermal insulation area ismade is a fluoridated resin. The heat insulation properties between theflexible area and the semiconductor substrate are enhanced andmanufacturing the semiconductor device is facilitated.

In a fifth aspect of the present invention, in the first to fourthaspect of the present invention, a reinforcement layer made of a hardermaterial than the material of which the thermal insulation area is madeis provided on at least one face orthogonal to a thickness direction ofthe thermal insulation area. The joint strength of the semiconductorsubstrate and the flexible area can be increased.

In a sixth aspect of the present invention, in the fifth aspect of thepresent invention, the reinforcement layer has a Young's modulus of9.8×10⁹ N/m² or more. The joint strength of the semiconductor substrateand the flexible area can be increased.

In a seventh aspect of the present invention, in the sixth aspect of thepresent invention, the reinforcement layer is a silicon dioxide thinfilm. The joint strength of the semiconductor substrate and the flexiblearea can be increased.

In an eighth aspect of the present invention, in the first to seventhaspect of the present invention, the portions of the semiconductorsubstrate and the flexible area in contact with the thermal insulationarea form comb teeth. The joint strength of the semiconductor substrateand the flexible area can be increased.

According to a ninth aspect of the present invention, there is provideda semiconductor device comprising a semiconductor device as the first toeighth aspect of the present invention and a moving element placedcontiguous with the flexible area, wherein when temperature of theflexible area changes, the moving element is displaced relative to thesemiconductor substrate. The semiconductor device which has similaradvantages to those in the invention as claimed in claims 1 to 8 as wellas can be driven with low power consumption can be provided.

In a tenth aspect of the present invention, in the ninth aspect of thepresent invention, the flexible area has a cantilever structure. Thesemiconductor device can be provided with large displacement of themoving element.

In an eleventh aspect of the present invention, in ninth aspect of thepresent invention, the moving element is supported by a plurality offlexible areas. The moving element can be supported stably.

In a twelfth aspect of the present invention, in the eleventh aspect ofthe present invention, the flexible areas are in the shape of a crosswith the moving element at the center. Good displacement accuracy of themoving element can be provided.

In a thirteenth aspect of the present invention, in the ninth aspect ofthe present invention, displacement of the moving element containsdisplacement rotating in a horizontal direction to a substrate face ofthe semiconductor substrate. The displacement of the moving elementbecomes large.

In a fourteenth aspect of the present invention, in the eleventh orthirteenth aspect of the present invention, the flexible areas are fourflexible areas each shaped like L, the four flexible areas being placedat equal intervals in every direction with the moving element at thecenter. The lengths of the flexible areas can be increased, so that thedisplacement of the moving element can be made large.

In a fifteenth aspect of the present invention, in the ninth tofourteenth aspect of the present invention, the flexible area is made upof at least two areas having different thermal expansion coefficientsand is displaced in response to the difference between the thermalexpansion coefficients. As the temperature of the flexible area ischanged, the flexible area can be displaced.

In a sixteenth aspect of the present invention, in the fifteenth aspectof the present invention, the flexible area includes an area made ofsilicon and an area made of aluminum. As the temperature of the flexiblearea is changed, the flexible area can be displaced because of thethermal expansion difference between aluminum and silicon.

In a seventeenth aspect of the present invention, in the fifteenthaspect of the present invention, the flexible area includes an area madeof silicon and an area made of nickel. As the temperature of theflexible area is changed, the flexible area can be displaced because ofthe thermal expansion difference between nickel and silicon.

In a eighteenth aspect of the present invention, in the fifteenth aspectof the present invention, at least one of the areas making up theflexible area is made of the same material as the thermal insulationarea. Since the flexible area and the thermal insulation area can beformed at the same time, the manufacturing process is simplified and thecosts can be reduced.

In a nineteenth aspect of the present invention, in the eighteenthaspect of the present invention, the flexible area includes an area madeof silicon and an area made of polyimide as the area made of the samematerial as the thermal insulation area. In addition to a similaradvantage to that in the invention, as the temperature of the flexiblearea is changed, the flexible area can be displaced because of thethermal expansion difference between silicon and polyimide, and the heatinsulation properties of the flexible area owing to polyimide.

In a twentieth aspect of the present invention the invention, in theeighteenth aspect of the present invention, the flexible area includesan area made of silicon and an area made of a fluoridated resin as thearea made of the same material as the thermal insulation area. Inaddition to a similar advantage, as the temperature of the flexible areais changed, the flexible area can be displaced because of the thermalexpansion difference between silicon and the fluoridated resin, and theheat insulation properties of the flexible area owing to the fluoridatedresin.

In a twenty-first aspect of the present invention, in the ninth tofourteenth aspect of the present invention, the flexible area is made ofa shape memory alloy. As the temperature of the flexible area ischanged, the flexible area can be displaced.

In a twenty-second aspect of the present invention, in the ninth totwenty-first aspect of the present invention, a thermal insulation areamade of a resin for joining the flexible area and the moving element isprovided between the flexible area and the moving element. The heatinsulation properties between the flexible area and the moving elementcan be provided and power consumption when the temperature of theflexible area is changed can be more suppressed.

In a twenty-third aspect of the present invention, in the twenty-secondaspect of the present invention, wherein rigidity of the thermalinsulation area provided between the semiconductor substrate and theflexible area is made different from that of the thermal insulation areaprovided between the flexible area and the moving element. Thedisplacement direction of the moving element can be determined dependingon the rigidity difference between the thermal insulation areas.

In a twenty-fourth aspect of the present invention, in the ninth totwenty-third aspects of the present invention, the flexible areacontains heat means for heating the flexible area. The semiconductordevice can be miniaturized.

In a twenty-fifth aspect of the present invention, in the ninth totwenty-fifth aspects of the present invention, wiring for supplyingpower to the heat means for heating the flexible area is formed withoutthe intervention of the thermal insulation area. The heat insulationdistance of the wiring can be increased and the heat insulationproperties of the flexible area can be enhanced.

In a twenty-sixth aspect of the present invention, in the ninth totwenty-fifth aspect of the present invention, the moving element isformed with a concave part. The heat capacity of the moving element islessened, so that the temperature change of the flexible area can beaccelerated.

In a twenty-seventh aspect of the present invention, in the ninth totwenty-sixth aspects of the present invention, a round for easing astress is provided in the proximity of the joint part of the flexiblearea and the moving element or the semiconductor substrate. The stressapplied in the proximity of the joint part when the flexible area isdisplaced is spread by means of the round, whereby the part can beprevented from being destroyed.

In a twenty-eighth aspect of the present invention, in thetwenty-seventh aspect of the present invention, the semiconductorsubstrate is formed with a projection part projecting toward the jointpart to the flexible area and the round is formed so that the shape ofthe round on the substrate face on the semiconductor substrate becomeslike R at both ends of the base end part of the projection part. Thestress applied to both ends of the base end part of the projection partwhen the flexible area is displaced is spread by means of the round,whereby the portion can be prevented from being destroyed.

In a twenty-ninth aspect of the present invention, in twenty-seventhaspect of the present invention, the semiconductor substrate is etchedfrom the substrate face to make a concave part, the flexible area isformed in a bottom face part of the concave part, and the round isformed so as to become shaped like R on the boundary between the bottomface part and a flank part of the concave part. The stress applied tothe boundary between the bottom face part and the flank part of theconcave part when the flexible area is displaced is spread by means ofthe round, whereby the portion can be prevented from being destroyed.

According to a thirtieth aspect of the present invention, there isprovided a semiconductor microvalve comprising a semiconductor device inany of ninth to twenty-ninth aspects and a fluid element being joined tothe semiconductor device and having a flow passage with a flowing fluidquantity changing in response to displacement of the moving element. Thesemiconductor microvalve which has similar advantages in ninth totwenty-ninth aspect of the present invention as well as can be drivenwith low power consumption can be provided.

In a thirty-first aspect of the present invention, in the thirties ofthe present invention, the semiconductor device and the fluid elementare joined by anodic junction. It is made possible to join thesemiconductor device and the fluid element.

In a thirty-second aspect of the present invention, in the thirtiesaspect of the present invention, the semiconductor device and the fluidelement are joined by eutectic junction. It is made possible to join thesemiconductor device and the fluid element.

In a thirty-third aspect of the present invention, in the thirtiethaspect of the present invention, the semiconductor device and the fluidelement are joined via a spacer layer. The thermal expansion differencebetween the semiconductor device and the fluid element when they arejoined is absorbed in the spacer layer and the stress applied to theflexible area can be suppressed.

In a thirty-fourth aspect of the present invention, in the thirty-thirdaspect of the present invention, the spacer layer is made of polyimide.The thermal expansion difference between the semiconductor device andthe fluid element when they are joined is absorbed because of elasticityof polyimide and the stress applied to the flexible area can besuppressed.

According to a thirty-fifth aspect of the present invention, there isprovided a semiconductor microrelay comprising a semiconductor device asthe ninth to twenty ninth aspect of the present invention and a fixedelement being joined to the semiconductor device and having fixedcontacts being placed at positions corresponding to a moving contactprovided on the moving element, the fixed contacts being able to come incontact with the moving contact. The semiconductor microrelay which hassimilar advantages to those in the invention as claimed in claims 9 to29 as well as can be driven with low power consumption can be provided.

In a thirty-sixth aspect of the present invention, in the thirty-fifthaspect of the present invention, the fixed contacts are placed away fromeach other and come in contact with the moving contact, whereby they arebrought into conduction via the moving contact. The semiconductormicrorelay wherein the fixed contacts placed away from each other can bebrought into conduction can be provided.

In a thirty-seventh aspect of the present invention, in the thirty-fifthor thirty-sixth aspect of the present invention, the moving contact andthe fixed contacts are gold cobalt. The moving contact and the fixedcontacts can be brought into conduction.

In a thirty-eighth aspect of the present invention, in the thirty-fifthto thirty-seventh aspect of the present invention, the semiconductordevice and the fixed element are joined by anodic junction. It is madepossible to join the semiconductor device and the fixed element.

In a thirty-ninth aspect of the present invention, in the thirty-fifthto thirty-seventh aspect of the present invention, the semiconductordevice and the fixed element are joined by eutectic junction. It is madepossible to join the semiconductor device and the fixed element.

In a fortieth aspect of the present invention, in the thirty-fifth tothirty-seventh aspect of the present invention, the semiconductor deviceand the fixed element are joined via a spacer layer. The thermalexpansion difference between the semiconductor device and the fluidelement when they are joined is absorbed in the spacer layer and thestress applied to the flexible area can be suppressed.

In a forty-first aspect of the present invention, in the fortieth aspectof the present invention, the spacer layer is made of polyimide. Thethermal expansion difference between the semiconductor device and thefluid element when they are joined is absorbed because of elasticity ofpolyimide and the stress applied to the flexible area can be suppressed.

According to a forty-second aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in theeighteenth aspect of the present invention prepared by a processcomprising the steps of:

etching and removing one face of the semiconductor substrate to form abottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate toform the concave part in the moving element;

etching and removing the other face of the semiconductor substrate toform at least a portion which becomes the thermal insulation area placedbetween the semiconductor substrate and the flexible area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

applying a coat of the thermal insulation material to the one face ofthe semiconductor substrate to form one area forming a part of theflexible area.

The thermal insulation area and one area forming a part of the flexiblearea are formed of the same material at the same time, whereby themanufacturing process is simplified and the costs can be reduced.

According to a forty-third aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in sixteenthaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form abottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate toform the concave part in the moving element;

etching and removing the other face of the semiconductor substrate toform at least a portion which becomes the thermal insulation area placedbetween the semiconductor substrate and the flexible area;

forming an aluminum thin film as an area defined in the flexible area onthe other face of the semiconductor substrate and a wire for applying anelectric power to the heating means;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area.

whereby the manufacturing process is simplified and the costs can bereduced.

According to a forty-fourth aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in seventeenthaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form abottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate toform the concave part in the moving element;

etching and removing the other face of the semiconductor substrate toform at least a portion which becomes the thermal insulation area placedbetween the semiconductor substrate and the flexible area;

forming a wire for applying an electric power to the heating means;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

forming a nickel thin film as an area defined in the flexible area onthe other face of the semiconductor substrate.

According to a forty-fifth aspect of the present invention there isprovided a manufacturing method of a semiconductor device in the firstaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form atleast a portion which becomes the thermal insulation area placed betweenthe semiconductor substrate and the flexible area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

etching and removing the other face of the semiconductor substrate toform the thermal insulation area.

According to a forty-sixth aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in the fifthaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form atleast a portion which becomes the thermal insulation area placed betweenthe semiconductor substrate and the flexible area;

forming a reinforce layer in the thermal insulation area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

etching and removing the other face of the semiconductor substrate toform the thermal insulation area.

This invention is carried out paying attention to the fact that a resinmaterial such as polyimide or a fluoridated resin has high heatinsulation properties (about 80 times those of silicon dioxide) andfurther is liquid and easy to work and that a thin film having anydesired thickness (several μm to several ten μm) can be easily providedby a semiconductor manufacturing process of spin coat, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a partially cutaway view in perspective of the structure of asemiconductor microactuator using a semiconductor device correspondingto a first embodiment of the invention;

FIG. 2(a) is a sectional view to show the structure of the semiconductormicroactuator in FIG. 1 and FIG. 2(b) is a top view to show thestructure of the semiconductor microactuator in FIG. 1;

FIG. 3 is a sectional view to show the structure of the semiconductordevice in FIG. 1;

FIGS. 4(a) to 4(c) show a structure model used to find the strength ofthe semiconductor device in FIG. 1; FIG. 4(a) is a schematic drawing,FIG. 4(b) is a distribution drawing, and FIG. 4(c) is a distributiondrawing;

FIGS. 5(a) to 5(d) are sectional views to show a manufacturing method ofthe semiconductor device in FIG. 1;

FIGS. 6(a) and 6(b) are a sectional view and a top view to show thestructure of another semiconductor device;

FIG. 7 is a sectional view taken on line Y-Y′ in FIG. 6(b) to show thestructure of the semiconductor device in FIGS. 6(a) and 6(b);

FIGS. 8(a) to 8(e) are sectional views to show a manufacturing method ofthe semiconductor device in FIGS. 6(a) and 6(b);

FIGS. 9(a) and 9(b) are a sectional view and a top view to show thestructure of still another semiconductor device;

FIG. 10 is a sectional view taken on line B-B′ in FIG. 9(b) to show thestructure of the semiconductor device in FIGS. 9(a) and 9(b);

FIG. 11 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a second embodiment of theinvention;

FIG. 12(a) is a sectional view to show the structure of thesemiconductor microactuator in FIG. 11 and FIG. 12(b) is a top view toshow the structure of the semiconductor microactuator in FIG. 11;

FIG. 13 is a sectional view to show the structure of anothersemiconductor microactuator;

FIGS. 14(a) to 14(e) are sectional views to show a manufacturing methodof the semiconductor microactuator in FIG. 13;

FIGS. 15(a) to 15(e) are sectional views to show a manufacturing methodof the semiconductor microactuator in FIG. 13;

FIG. 16 is a sectional view to show another wiring structure of thesemiconductor microactuator in FIG. 13;

FIG. 17 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a third embodiment of theinvention;

FIG. 18 is a top view to show the structure of the semiconductormicroactuator corresponding to the third embodiment of the invention;

FIG. 19 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a fourth embodiment of theinvention;

FIG. 20 is a top view to show the structure of the semiconductormicroactuator corresponding to the fourth embodiment of the invention;

FIG. 21 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a fifth embodiment of theinvention;

FIG. 22 is a top view to show the structure of the semiconductormicroactuator corresponding to the fifth embodiment of the invention;

FIG. 23 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a sixth embodiment of theinvention;

FIG. 24 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to a seventh embodiment of theinvention;

FIG. 25 is a partially cutaway view in perspective of the structure of asemiconductor microactuator corresponding to an eighth embodiment of theinvention;

FIG. 26 is a partially cutaway view in perspective of the structure ofanother semiconductor microactuator;

FIG. 27 is a partially cutaway view in perspective of the structure of asemiconductor microvalve corresponding to a ninth embodiment of theinvention;

FIG. 28 is a partially cutaway view in perspective of the structure ofanother semiconductor microvalve;

FIG. 29 is a partially cutaway view in perspective of the structure ofstill another semiconductor microvalve;

FIG. 30 is a partially cutaway view in perspective of the structure of asemiconductor microvalve corresponding to a tenth embodiment of theinvention;

FIG. 31 is a partially cutaway view in perspective of the structure ofanother semiconductor microvalve;

FIG. 32 is a partially cutaway view in perspective of the structure of asemiconductor microrelay corresponding to an eleventh embodiment of theinvention;

FIG. 33 is a partially cutaway view in perspective of the structure of asemiconductor microrelay corresponding to a twelfth embodiment of theinvention;

FIGS. 34(a) to 34(d) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 33;

FIGS. 35(a) to 35(e) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 33;

FIGS. 36(a) and 36(b) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 33;

FIG. 37 is a partially cutaway view in perspective of the structure ofanother semiconductor microrelay;

FIG. 38 is a perspective view used to describe the function of thesemiconductor microrelay in FIG. 33;

FIG. 39 is a relation drawing used to describe the function of thesemiconductor microrelay in FIG. 33;

FIG. 40 is a side view used to describe the function of thesemiconductor microrelay in FIG. 33;

FIG. 41 is a partially cutaway view in perspective of the structure of asemiconductor microrelay corresponding to a thirteenth embodiment of theinvention;

FIGS. 42(a) to 42(d) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 41;

FIGS. 43(a) to 43(e) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 41;

FIGS. 44(a) and 44(b) are sectional views to show a manufacturing methodof the semiconductor microrelay in FIG. 33;

FIGS. 45(a) to 45(d) are sectional views to show another manufacturingmethod of the semiconductor microrelay in FIG. 41;

FIGS. 46(a) to 46(e) are sectional views to show another manufacturingmethod of the semiconductor microrelay in FIG. 41;

FIGS. 47(a) and 47(b) are sectional views to show another manufacturingmethod of the semiconductor microrelay in FIG. 33;

FIG. 48 is a partially cutaway view in perspective of the structure ofanother semiconductor microrelay;

FIG. 49 is a perspective view used to describe the function of thesemiconductor microrelay in FIG. 41;

FIG. 50 is a relation drawing used to describe the function of thesemiconductor microrelay in FIG. 41;

FIG. 51 is a relation drawing used to describe the function of thesemiconductor microrelay in FIG. 41;

FIG. 52 is a partially cutaway view in perspective of the structure ofanother semiconductor microrelay;

FIG. 53 is a top view to show the structure of a semiconductormicroactuator in a related art;

FIG. 54 is a sectional view to show the structure of the semiconductormicroactuator in the related art;

FIG. 55 is a sectional view to show the structure of a semiconductormicrorelay in a related art; and

FIG. 56 is a schematic drawing used to describe the function of thesemiconductor microrelay in the related art.

FIG. 57 is a partially cutaway view in perspective of the structure of asemiconductor microactuator using a semiconductor device correspondingto another embodiment of the invention;

FIG. 58(a) is a sectional view to show the structure of thesemiconductor microactuator in FIG. 57;

FIG. 58(b) is a top view to show the structure of the semiconductormicroactuator in FIG. 57;

FIG. 59 is a partially cutaway view in perspective of the structure of asemiconductor microactuator using a semiconductor device correspondingto another embodiment of the invention;

FIG. 60 is a top view to show the structure of the semiconductormicroactuator in FIG. 59;

FIG. 61 is a partially cutaway view in perspective of the structure of asemiconductor microvalve using a semiconductor device corresponding toanother embodiment of the invention; and

FIG. 62 is a partially cutaway view in perspective of the structure of asemiconductor microvalve using a semiconductor device corresponding toanother embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Principal of Present Invention

However, the semiconductor microactuator having the structure shown inU.S. Pat. No. 5,069,419 involves the following problem: First, thethermal insulation effect of the hinge structure of the silicon dioxidethin film will be considered. Generally, heat quantity Q escaping from ahigh-temperature portion to a low-temperature portion is

Q(W)=−λ(t ₂ −t ₁)/δ)A  (Expression X)

where Q: Heat quantity (heat move speed)

t₂−t₁: Temperature difference (° C.)

δ: Distance from heat source (cm)

A: Cross section perpendicular to direction of heat flow (cm²)

λ: Heat conductivity (J/cm s° C.)

Then, the relational expression is used to calculate the heat quantityescaping from the diaphragm 300 to the silicon frame 302. Letting thetemperature difference between the diaphragm 300 and the silicon frame302 be 150° C., the width of the hinge 303 be 30 μm, the diameter of thediaphragm 200 be 2.5 mm, and the thickness of the hinge 303 be 2 μm(estimated from “Electrically-Activated, Micromachined Diaphragm Valves”Technical Digest IEEE Solid-State Sensor and Actuator Workshop, pp65-69,June 1990), cross section perpendicular to the direction of heat flow,A1, is

A 1=2.5 mm×π×2 μm=0.25 cm×π×2×10⁻⁴ cm=1.57×10⁻⁴ cm²

Since the heat conductivity λ of silicon dioxide equals 0.0084 (W/cm°C.), escape heat quantity Q1 isQ1 = 0.084(W/cm  ^(^(∘))C.) × 150^(^(∘))  C./(30 × 10⁻⁴  cm) × 1.57 × 10⁻⁴  cm² = 0.66  W = 600  mW

Next, the heat quantity escaping from the diaphragm 300 to the siliconframe 302 if the hinge structure of silicon dioxide is not provided iscalculated. Letting the thickness of the silicon diaphragm 300 be 10 μm,cross section perpendicular to the direction of heat flow, A2, iscalculated as follows:

A 2=2.5 mm×π×10 μm=0.25 cm×π×10×10⁻⁴ cm=7.85×10⁻⁴ cm²

Since the heat conductivity λ of silicon equals 1.48 (W/cm° C.), escapeheat quantity Q2 is

Q 2=1.48(W/cm° C.)×150° C./(30×10⁻⁴ cm)×7.85×10⁻⁴ _(cm) ²=58 W

Then, the hinge 303 of silicon dioxide thin film is provided, wherebyabout 90-times thermal insulation effect can be produced. Thus, thesemiconductor microactuator described in U.S. Pat. No. 5,069,419 has astructure with better thermal efficiency than that of the conventionalstructure. However, considering the current state of application, it isdesired to furthermore decrease the heat loss. Specifically, the heatescape (heat loss) is thought of as power (consumption power) suppliedall the time to maintain the diaphragm 300 at a predeterminedtemperature (for example, 150° C.).

In the semiconductor microactuator described in U.S. Pat. No. 5,069,419,the silicon dioxide thin film is thick as 2 μm in the part of the hinge303. The factor for determining the thickness of the silicon dioxidethin film of the hinge 303 is not clearly described in thespecification. However, if the semiconductor microactuator described inU.S. Pat. No. 5,069,419 is used with a microvalve, etc., it isconceivable that pressure applied to a moving element will concentrateon the hinge 303, and a film thickness is required to such an extentthat the hinge 303 is not broken under the pressure. However, if thefilm thickness of the hinge 303 is increased, the thermal insulationeffect is reduced as shown in the heat escape calculation expression(expression X). Then, it can be estimated that the thickness of thesilicon dioxide thin film having a reasonable strength and producing athermal insulation effect is determined 2 μm.

By the way, the semiconductor microactuator described in U.S. Pat. No.5,069,419 is of a moving structure with bimetal made up of the silicondiaphragm 300 and the aluminum thin film 304 as described in thespecification; to provide electric insulation, a silicon dioxide thinfilm 306 is inserted between the diaphragm 300 and the aluminum thinfilm 304.

In a semiconductor manufacturing process, it is desired that the silicondioxide thin film 306 and the silicon dioxide thin film of the hinge 303are formed at the same time and have the same film thickness. However,if the film thickness of the silicon dioxide thin film 306 insertedbetween the diaphragm 300 and the aluminum thin film 304 becomes thickas 2 μm, it is conceivable that the bimetal characteristic of the drivesource will degraded. In the example described in the document“Electrically-Activated, Micromachined Diaphragm Valves” TechnicalDigest IEEE Solid-State Sensor and Actuator Workshop, pp65-69, June1990, the aluminum thin film 304 has a film thickness of 5 to 6 μm andif the silicon dioxide thin film 306 having a film thickness of 2 μm isinserted between the diaphragm 300 and the aluminum thin film 304, itcan be easily estimated that the silicon dioxide thin film 306 willbecome a factor for hindering bending of the diaphragm 300 at theheating time.

In the semiconductor manufacturing process, normally a thin film ofsilicon dioxide is formed at a high temperature of about 2000° C. Thus,considering the thermal expansion coefficients of silicon and silicondioxide, it is possible that a considerable internal stress occursbetween the silicon diaphragm 300 and the silicon dioxide thin film 306.As the silicon dioxide thin film 306 becomes thicker, the internalstress grows, causing the bimetal characteristic to be degraded. Thus,the silicon dioxide thin film 306 between the diaphragm 300 and thealuminum thin film 304 must be thinned as much as possible (2×10⁻⁸ m(200 A)) and the silicon dioxide film of the hinge 303 must be madethick to some extent (2 μm). However, formation of such a thin filmstructure of silicon dioxide requires a very complicated semiconductormanufacturing process. The manufacturing process is not mentioned in thespecification of U.S. Pat. No. 5,069,419.

As a remedy, another hinge structure is disclosed in U.S. Pat. No.5,271,597, wherein the thin film structure of silicon dioxide asdescribed above is not adopted and a silicon dioxide thin film of ahinge part and a silicon dioxide thin film between a diaphragm and analuminum thin film have the same film thickness. In this method, thesilicon dioxide thin film of the hinge part is thinned and to make upfor reduction in the strength of the hinge part as the film is thinned,silicon of a part of the diaphragm is used for bonding the diaphragm anda silicon frame in addition to the hinge, thus the thermal insulationeffect is reduced and a structure for lessening power consumption of thesemiconductor microactuator is not provided. Thus, a large number ofproblems remain to be solved in the thermal insulation structure in thesemiconductor microactuator.

As an example of a semiconductor microvalve in a related art, amicrominiature valve is described in U.S. Pat. No. 5,058,856. Thismicrominiature valve also uses a semiconductor microactuator comprisingat least two materials having different thermal expansion coefficientsin combination as a bimetal structure wherein the bimetal structure isheated and the difference between the thermal expansion coefficients isused to provide displacement. The microactuator has a thermal insulationstructure provided by placing a torsion bar suspension. This structureminimizes the heat loss to a silicon frame because of a decrease in thecross section perpendicular to a heat flow and an increase in the lengthof a passage through which the heat flow passes. However, since thetorsion bar suspension structure is formed of silicon, it is consideredthat a sufficient thermal insulation effect cannot be produced asdiscussed in the calculation of heat escape.

This can be estimated from a microvalve performance comparison tabledescribed in the document “SILICON MICROVALVES FOR GAS FLOW CONTROL” The8th International Conference on Solid-State Sensor and Actuators,Stockholm, Sweden, 1995, p276-279. This document compares a microvalveinvolving the “semiconductor microactuator” disclosed in U.S. Pat. No.5,069,419 with a microvalve related to the “microminiature valve”disclosed in U.S. Pat. No. 5,058,856; the latter has pressure resistancesix times that of the former and flow quantity range 10 times that ofthe former, but power consumption about twice that of the former andheat resistance about a third that of the former.

Thus, the microminiature valve disclosed in U.S. Pat. No. 5,058,856 hasa structure capable of generating a large force because of the torsionbar suspension structure formed of silicon, but consumes larger power.

First Embodiment

A first embodiment of the invention will be discussed. FIG. 1 is apartially cutaway view in perspective of the structure of asemiconductor microactuator using a semiconductor device according tothe invention. FIG. 2A is a sectional view and FIG. 2B is a top view.

As shown in the figures, a semiconductor microactuator 1 includes asemiconductor substrate 3 which becomes a hollow frame shaped roughlylike a quadrangle, four thin portions 2S each shaped roughly like aquadrangle piece, the thin portions 2S separated from the semiconductorsubstrate 3 with one ends connected via thermal insulation areas 7inwardly roughly from the centers of the sides of the semiconductorsubstrate 3, a moving element 5 formed like a hollow quadrangularprismoid with the top face opened like a quadrangle and narrower towardthe bottom, the moving element 5 having top opening margins connected toopposite ends of the thin portions 2S, and thin films 2M of aluminumthin films, nickel thin films, or the like placed on the top faces ofthe thin portions 2S, the thin films 2M and the thin portions 2S makingup flexible areas 2.

The semiconductor substrate 3, the thin portions 2S, and the movingelement 5 are formed, for example, by working a semiconductor substrateof a silicon substrate, etc. Each thin portion 2S is formed on a surfacewith an impurity-diffused resistor 6 (diffused resistor 6) of heatingmeans. Power is supplied to the diffused resistors 6 by wiring 4 aconnected to electrode pads 4 placed at the four corners of thesemiconductor substrate 3 and the temperatures of the diffused resistors6 rise, heating the flexible areas 2 each made up of the thin portion 2Sand the thin film 2M. The thin film 2M is made of aluminum, nickel, orthe like as described above and the thin portion 2S is made of silicon,etc.; the thin film 2M and the thin portion 2S have different thermalexpansion coefficients.

Each thermal insulation area 7 for joining the semiconductor substrate 3and the flexible area 2 has roughly the same thickness as the thinportion 2S and is made of a thermal insulation material such as afluoridated resin or polyimide for thermally insulating thesemiconductor substrate 3 and the flexible area 2. Of the electrode pads4 placed at the four corners of the semiconductor substrate 3, theelectrode pads 4 in the upper-right corner and the lower-left corner inFIG. 2B are connected to an external power supply and the series circuitof two diffused resistors 6 is connected in parallel to power supply.

The four flexible areas 2 are in the shape of a cross with the movingelement 5 at the center and the surroundings of the moving element 5 aresupported by the flexible areas 2. The semiconductor substrate 3, theflexible areas 2, and the thermal insulation areas 7 each between thesemiconductor substrate 3 and the flexible area 2 make up asemiconductor device 8.

In the described semiconductor microactuator 1, upon application ofpower to the diffused resistors 6, the temperature rises, heating theflexible areas 2, and a thermal stress occurs because of the differencebetween the thermal expansion coefficients of the thin film 2M and thethin portion 2S making up each flexible area 2. For example, if metalthin films of aluminum, nickel, etc., are formed as the thin films 2M,the metal of aluminum, nickel, etc., has a lager thermal expansioncoefficient than silicon forming the thin portions 2S, so that theflexible areas 2 are bent downward in the figure. The moving element 5placed contiguous with the flexible areas 2 receives the thermal stressof the flexible areas 2 and is displaced downward with respect to thesemiconductor substrate 3.

As described above, the semiconductor microactuator 1 includes the fourflexible areas 2 in the shape of a cross with the moving element 5 atthe center and displacement of the moving element 5 becomes irrotationaldisplacement relative to the semiconductor substrate 3; good controlaccuracy of displacement is provided and a large force can be generated.As described above, each flexible area 2 is formed on the surface withthe diffused resistor 6 for heating the flexible area 2, namely,contains the diffused resistor 6, so that the semiconductormicroactuator 1 can be miniaturized.

The semiconductor microactuator 1 of the embodiment includes eachflexible area 2 made up of two areas having different thermal expansioncoefficients, namely, the thin portion 2S and the thin film 2M, but theinvention is not limited to it. For example, each flexible area 2 may bemade of a shape memory alloy of nickel titanium, etc., and the flexiblearea 2 made of a shape memory alloy may be displaced because oftemperature change.

Of course, this invention is limited for use of semiconductormicroactuator. It is applicable for a temperature sensor in such amanner that the displacement of the flexible area caused by changing thetemperature is measured by, for example, the laser displacement deviceto detect the temperature in accordance with the displacement of theflexible area. Namely the present invnetion is applied to thesemiconductor device using the effect such that the thermal insulationarea 7 is provided between each flexible area 2 and the semiconductorsubstrate 3, so that the semiconductor microactuator 1 has the advantagethat heat produced when the flexible areas 2 are heated can be preventedfrom escaping to the semiconductor substrate 3.

To describe the function of the semiconductor device 8 used with thesemiconductor microactuator 1 of the invention, the case where thelength and the thickness in the joint direction of the semiconductorsubstrate 3 and the flexible area 2 in the thermal insulation area 7 are30 μm and 20 μm respectively and polyimide is used as the material asshown in FIG. 3, which is a sectional view of the semiconductor device8, will be discussed as a specific example. Assume that the length inthe joint direction of the flexible area 2 shown in FIG. 1 is 800 μm andthe width of the flexible area 2 (length in the direction orthogonal tothe joint direction) is 600 μm.

Heat quantity Q3 escaped from the flexible area 2 through the thermalinsulation area 7 to the semiconductor substrate 3 is calculatedaccording to the expression X shown in the description of the relatedart. Here, cross section perpendicular to the direction of the heat flowof escape heat, A10, is

A 10=(thickness of polyimide)×(width of flexible area)=20 μm×600μm=1.2×10⁻⁴ cm²

The heat conductivity of polyimide is 1.17×10⁻³ (W/cm° C.) and thedistance from the heat source, δ, namely, the distance between theflexible area 2 and the semiconductor substrate 3 is 30 μm. Thus, theheat quantity Q3 escaped from the flexible area 2 heated to 150° C. tothe semiconductor substrate 3 isQ3 = 1.17 × 10⁻³(W/cm  ^(^(∘))C.) × (150^(^(∘))  C./(30 × 10⁻⁴  cm)) × 1.2 × 10⁻⁴(cm²) = 4.2 × 10⁻³(W) = 4.2  (mW)

Since the semiconductor device 8 has the four flexible areas 2 asdescribed above, the heat quantity becomes 16.8 mW as a whole. Thisindicates that the temperature of the flexible area 2 can be maintainedat 150° C. by feeding input power 16.8 mW into the diffused resistor 6;the power consumption can be reduced to {fraction (1/40)} as comparedwith 660 mW in the related art.

Next, the strength of the thermal insulation area 7 made of polyimidewill be discussed. A model of a twin-cantilever structure with both endsfixed shown in FIG. 4A will be considered. If load W is imposed on thecenter of a beam 21 (corresponding to the flexible area 2) from below asshown in FIG. 4A, the shearing force and moment force of the beam 21become as shown in FIGS. 4B and 4C respectively. In FIG. 4A, the thermalinsulation area 7 is positioned either between a fixed end 22 a and thebeam 21 or between a fixed end 22 b and the beam 21. Then, a forceapplied to the beam 21 is found, for example, if l-g load W is imposedon the center of the beam 21 (corresponding to the case where a pressureof 46.7 kPa is put on an orifice 500 μm for a microvalve).

Shearing force applied to the beam, F1, is

F1=W/2=1.0×10⁻³ (kgf)/2=0.5×10⁻³ (kgf)=4.9×10⁻³ (N), and maximumshearing strength applied to the beam, Fmax, is Fmax=F1/S1 (where S1 isthe cross-sectional area of the beam). Here, letting width b1 of thebeam 21 be 600 μm and thickness h1 of the beam 21 be 20 μm, thecross-sectional area S1 is

S1=(b1)(h1)=600×10⁻4×20×10⁻⁴=1.2×10⁻⁴ cm². Therefore, the maximumshearing strength applied to the beam 21, Fmax, is Fmax=0.50×10⁻³(kgf)/1.2×10⁻⁴ (cm²)=4.16 (kgf/cm²)=4.16×0.098 (MPa)=0.41 (MPa). Next,maximum stress applied to the beam 21, σmax, is found. The maximumstress σmax is represented as σmax=Mmax/Z1 where Mmax is the maximummoment and Z1 is a section modulus. The maximum moment Mmax equals WL/8(where L is the length of the beam, 800 μm) as shown in FIG. 4C.Therefore, the maximum moment Mmax

Mmax=WL/8=1.0×10⁻³ (kgf)×800×10⁻⁴ (cm)/8=1.0×10⁻⁵ (kgf cm)=9.8×10⁻⁵ (Ncm). The section modulus Z1 is

Z1=(b1)(h1)²/6=⅙×600×10⁻⁴×(20×10⁻⁴)²=4.0×10⁻⁸ (cm³).

Then, the maximum stress σmax based on the moment isσ  max  = M  max /Z = 1.0 × 10⁻⁵(kgf  cm)/4.0 × 10⁻⁸(cm³) = 250(kgf/cm²) = 24.5  (MPa).

The beam 21 is 600 μm wide and 800 μm long as described above.

Since polyimide has a disruptive strength of about 30 MPa, asemiconductor microactuator capable of resisting a load of about 1 g inthe thermal insulation area 7 described above can be provided. Thestrength of the thermal insulation area 7 can be enhanced as shown inanother example. Although not described, a similar advantage can also beexpected with a fluoridated resin.

A formation method example of the thermal insulation area 7 will bediscussed with reference to FIGS. 5A to 5D. First, as shown in FIG. 5A,the portion corresponding to a thermal insulation area on the surface ofa semiconductor substrate 17 is etched with KOH, etc., to form a groove15. Then, as shown in FIG. 5B, a coat of a polyimide thin film 16 isrotationally applied with a coater, etc., so as to fill the groove 15.Next, as shown in FIG. 5C, patterning is performed by executing asemiconductor photolithography process, etc., so that the polyimide thinfilm 16 of the portion filling the groove 15 is left and that otherportions are removed, and heating is executed to about 400° C. toevaporate an organic solvent, etc., contained in polyimide and cure.Next, as shown in FIG. 5D, etching with KOH, etc., is performed from therear face of the semiconductor substrate 17. In FIG. 5D, numeral 19denotes a semiconductor substrate which becomes a frame and numeral 20denotes a flexible area. The thermal insulation area 7 is formed throughsuch a process.

Thus, the thermal insulation area 7 is formed between the flexible area2 and the semiconductor substrate 8 utilizing the nature that the resinmaterial of polyimide, fluoridated resin, etc., has high thermalinsulation properties (thermal conductivity coefficient: 0.4 W/(m° C.)or less, about 80 times that of silicon dioxide) and is liquid and easyto work and can be easily formed to be a thin film of a desiredthickness (several μm to several ten μm) by executing a semiconductormanufacturing process of spin coat, etc. Therefore, a semiconductordevice having an excellent thermal insulation effect and strength ascompared with the example in the related art can be easily providedusing the semiconductor manufacturing process. As described above, thethermal insulation area 7 is made almost as thick as the thin portion 2Sof the flexible area 2, whereby the semiconductor substrate 3 and theflexible area 2 are joined reliably and the strength of the jointportion can be enhanced.

The semiconductor microactuator 1 using the semiconductor device 8comprising such advantages, which is easily manufactured and has highthermal insulation properties, prevents heat generated by the diffusedresistors 6 from escaping and can be driven with low power consumption,namely, can be driven with a battery and thus can be miniaturized.

Next, another configuration example of the semiconductor device 8 willbe discussed. As shown in FIGS. 6A and 6B, the example semiconductordevice 8 is the same as the semiconductor device in FIG. 3 in that athermal insulation area 7 made of a thermal insulation material such asa fluoridated resin or polyimide is formed between a semiconductorsubstrate 3 and a flexible area 2; the former differs from the latter inthat the thermal insulation area 7 is formed on a bottom face (faceorthogonal to the thickness direction) with a reinforcement layer 12made of a harder material than the material forming the thermalinsulation area 7, such as a silicon dioxide thin film (Young's modulus:9.8×10⁻⁹ N/m² or more). FIG. 6A is a sectional view and FIG. 6B is a topview. FIG. 7 is a sectional view taken on line Y-Y′ in FIG. 6B.

Specifically, as shown in FIG. 7, the thermal insulation area 7 is 19 μmthick and the reinforcement layer 12 is 1 μm thick. As shown in FIG. 6A,the length in the joint direction of the semiconductor substrate 3 andthe flexible area 2 in the thermal insulation area 7 is 30 μm and thelength in the Y-Y′ direction, namely, in the depth direction is 600 μm.Here, the strength of the thermal insulation area 7 to use polyimide asthe material forming the thermal insulation area 7 and silicon dioxideas the material forming the reinforcement layer 12 is calculated undersimilar conditions to those of the strength calculation of the thermalinsulation area 7 in FIG. 3 described above.

Letting the Young's modulus of the material of each of the thermalinsulation area 7 and the reinforcement layer 12 be E_(i) and thecross-sectional area of the cross section of each area shown in FIG. 7be A_(i), the distance from the bottom face to the neutral axis, ηa, isgiven by the following expression: $\begin{matrix}{{\eta \quad a_{i}} = \frac{\sum\limits_{i}^{\quad}{E_{i}{\int{\eta \quad {dA}_{i}}}}}{\sum\limits_{i}^{\quad}{E_{i} \cdot A_{i}}}} & \left\lbrack {{Expression}\quad 1} \right\rbrack\end{matrix}$

The values are found with respect to silicon dioxide forming thereinforcement layer 12 as follows: $\begin{matrix}{{{{{{Young}'}s\quad {modulus}\quad E_{s}};{7.3 \times 10^{10}\left( {N/m^{2}} \right)}}\quad {{{Cross}\text{-}{sectional}\quad {area}\quad A_{s}};{1 \times 10^{- 6} \times 600 \times 10^{- 6}\left( m^{2} \right)}}\quad {{E_{s} \cdot A_{s}} = {{7.3 \times 10^{10}\left( {N/m^{2}} \right) \times 1 \times 10^{- 6} \times 600 \times 10^{- 6}\left( m^{2} \right)}\quad = {{43.8N}\quad \begin{matrix}{{E_{s}{\int{\eta \quad {dA}_{s}}}} = {E_{s}{\int_{0}^{1\quad \mu \quad m}{\eta \left( {600 \times 10^{- 6}d\quad \eta} \right)}}}} \\{= {7.3 \times 6 \times 10^{6} \times \left\lbrack {\eta^{2}/2} \right\rbrack_{0}^{1\mu \quad m}}} \\{= {{21.9 \times 10^{- 6}N} - m}}\end{matrix}}}}}\quad} & \left\lbrack {{Expression}\quad 2} \right\rbrack\end{matrix}$

The values are found with respect to polyimide forming the thermalinsulation area 7 as follows: $\begin{matrix}{{{{{Young}'}s\quad {modulus}\quad E_{f}};{5.0 \times 10^{8}\left( {N/m^{2}} \right)}}\quad {{{Cross}\text{-}{sectional}\quad {area}\quad A_{f}};{19 \times 10^{- 6} \times 600 \times 10^{- 6}\left( m^{2} \right)}}\quad {{E_{f} \cdot A_{f}} = {{5.0 \times 10^{8}\left( {N/m^{2}} \right) \times 19 \times 10^{- 6} \times 600 \times 10^{- 6}\left( m^{2} \right)}\quad = {5.70N}}}\quad \begin{matrix}{{E_{f}{\int{\eta \quad {dA}_{f}}}} = {E_{f}{\int_{1\mu \quad m}^{20\quad \mu \quad m}{\eta \left( {600 \times 10^{- 6}d\quad \eta} \right)}}}} \\{= {5.0 \times 6 \times 10^{4} \times \left\lbrack {\eta^{2}/2} \right\rbrack_{1\mu \quad m}^{20\quad \mu \quad m}}} \\{= {59.8 \times 10^{- 6}N\text{-}m}}\end{matrix}} & \left\lbrack {{Expression}\quad 3} \right\rbrack\end{matrix}$

Using the found values, the distance to the neutral axis, ηa, is foundas follows: $\begin{matrix}{{{\eta \quad a} = {\frac{\sum\limits_{i}^{\quad}{E_{i}{\int{\eta \quad {dA}_{i}}}}}{\sum\limits_{i}^{\quad}{E_{i} \cdot A_{i}}} = {\frac{\left( {21.9 + 59.8} \right) \times 10^{- 6}}{\left( {42.8 + 5.7} \right)} = {{1.68 \times 10^{- 6}(m)} = {1.68\quad {\mu m}}}}}}\quad} & \left\lbrack {{Expression}\quad 4} \right\rbrack\end{matrix}$

Next, secondary moments I_(s) and I_(f) concerning the neutral axes ofsilicon dioxide and polyimide are found as follows: $\begin{matrix}{\begin{matrix}{I_{s} = {{\int{\eta_{i}^{2}{dA}_{i}}} = {\int_{0.66\quad {\mu m}}^{1.68\quad {\mu m}}{\eta_{i}^{2}\left( {600 \times 10^{- 6}d\quad \eta_{i}} \right)}}}} \\{= {600 \times 10^{- 6} \times \left\lbrack {\eta^{3}/3} \right\rbrack_{{- 0.68}\quad {\mu m}}^{1.68\quad {\mu m}}}} \\{= {8.86 \times 10^{- 22}m^{4}}}\end{matrix}\begin{matrix}{I_{f} = {{\int{\eta_{i}^{2}{dA}_{i}}} = {\int_{0.68\quad {\mu m}}^{18.32\quad {\mu m}}{\eta_{i}^{2}\left( {600 \times 10^{- 6}d\quad \eta_{i}} \right)}}}} \\{= {600 \times 10^{- 6} \times \left\lbrack {\eta^{3}/3} \right\rbrack_{{- 0.68}\quad {\mu m}}^{18.32\quad {\mu m}}}} \\{= {1.22 \times 10^{- 18}m^{4}}}\end{matrix}} & \left\lbrack {{Expression}\quad 5} \right\rbrack\end{matrix}$

Here, ηi=η−ηa, namely, ηi denotes the distance from the neutral axis. Aspreviously described with reference to FIGS. 4A to 4C, if a load of 1 gis imposed on the center of the beam with both ends fixed, the maximummoment Mmax applied to the beam is Mmax=1.00×10⁻⁵ (kgfcm)=9.8×1.00×10⁻⁵×10⁻² (N m)=9.8×10⁻⁷ (N m).

The maximum bending stress of silicon dioxide, σsmax, is calculated asfollows: $\begin{matrix}\begin{matrix}{\sigma_{s\quad \max} = {M_{\max}\frac{E_{s} \cdot \eta_{i}}{\sum\limits_{i}^{\quad}{E_{i} \cdot I_{i}}}}} \\{= \frac{0.98 \times 10^{- 6} \times 7.3 \times 10^{10} \times 1.68 \times 10^{- 6}}{{7.3 \times 10^{10} \times 8.86 \times 10^{- 22}} + {5 \times 10^{8} \times 1.22 \times 10^{- 18}}}} \\{= {{1.78 \times 10^{8}\left( {{kg}\text{/}m^{2}} \right)} = {178\quad ({MPa})}}}\end{matrix} & \left\lbrack {{Expression}\quad 6} \right\rbrack\end{matrix}$

Here, I_(i) denotes each of the secondary moments I_(s) and I_(f). Themaximum bending stress of polyimide, σfmax, is calculated as follows:$\begin{matrix}\begin{matrix}{\sigma_{f\quad \max} = {M_{\max}\frac{E_{f} \cdot \eta_{i}}{\sum\limits_{i}^{\quad}{E_{i} \cdot I_{i}}}}} \\{= \frac{0.98 \times 10^{- 6} \times 5.0 \times 10^{8} \times 18.32 \times 10^{- 6}}{{7.3 \times 10^{10} \times 8.86 \times 10^{- 22}} + {5 \times 10^{8} \times 1.22 \times 10^{- 18}}}} \\{= {{1.33 \times 10^{7}\left( {{kg}\text{/}m^{2}} \right)} = {13.3\quad ({MPa})}}}\end{matrix} & \left\lbrack {{Expression}\quad 7} \right\rbrack\end{matrix}$

Therefore, the stress applied to the thermal insulation area 7 made ofpolyimide becomes about a half that in the example shown in FIG. 3.Apparently, it is equivalent to twice the strength. In FIG. 6, thereinforcement layer 12 is provided on the bottom face of the thermalinsulation area 7, but if the reinforcement layer 12 is provided on thetop face of the thermal insulation area 7, a similar effect can beproduced if the direction is a direction orthogonal to the thicknessdirection. If the reinforcement layer 12 is provided on both the top andbottom faces of the thermal insulation area 7, twice the effect producedby providing the reinforcement layer 12 on either the top or bottom faceof the thermal insulation area 7 can be produced.

A formation method example of the thermal insulation area 7 shown inFIGS. 6A and 6B will be discussed with reference to FIGS. 8A to 8E.First, as shown in FIG. 8A, the portion corresponding to a thermalinsulation area on the surface of a semiconductor substrate 17 a isetched with KOH, etc., to form a groove 15 a. Then, as shown in FIG. 8B,a silicon dioxide thin film 18 is formed on the surface of thesemiconductor substrate 17 a by thermal oxidation, etc. The silicondioxide thin film 18 is removed except the surface portion of the groove15 a by etching, etc.

Next, as shown in FIG. 8C, a coat of a polyimide thin film 16 a isrotationally applied with a coater, etc., so as to fill the groove 15 a.Next, as shown in FIG. 8D, patterning is performed by executing asemiconductor photolithography process, etc., so that the polyimide thinfilm 16 a of the portion filling the groove 15 a is left and that otherportions are removed, and heating is executed to about 400° C. toevaporate an organic solvent, etc., contained in polyimide and cure.Next, as shown in FIG. 8E, etching with KOH, etc., is performed from therear face of the semiconductor substrate 17 a, thereby forming thethermal insulation area. In FIG. 8E, numeral 19 a denotes asemiconductor substrate which becomes a frame and numeral 20 a denotes aflexible area.

Next, still another configuration example of semiconductor device of theinvention will be discussed. As shown in FIG. 9B, which is a top view, athermal insulation area 10 is provided between a semiconductor substrate3 and a flexible area 2 and the portions of the semiconductor substrate3 and the flexible area 2 in contact with the thermal insulation area 10form comb teeth in the joint direction of the semiconductor substrate 3and the flexible area 2 (orthogonal direction to line B-B′). As shown inFIG. 10, which is a sectional view taken on line B-B′ in FIG. 9B, theflexible area 2, the semiconductor substrate 3, and the thermalinsulation area 10 are mixed in the B-B′ direction. The thermalinsulation area 10 is formed of a fluoridated resin, polyimide, etc.

To calculate the strength of the thermal insulation area 10, let thethickness of the thermal insulation area 10 be 20 μm and the width in adirection perpendicular to the B-B′ direction be 30 μm, as shown inFIGS. 9A and 9B, as a specific example. As shown in FIG. 10, let thewidth in the B-B′ direction of each comb tooth consisting of theflexible area 2 and the semiconductor substrate 3 be 180 μm and thewidth in the B-B′ direction of the thermal insulation area 10 be 30 μm.The material of the thermal insulation area 10 is polyimide and thesemiconductor substrate 3 and the flexible area 2 are formed of silicon.The strength of the thermal insulation area 10 is calculated undersimilar conditions to those of the strength calculation in FIG. 3 forcomparison.

For a structure comprising silicon and polyimide in combination as shownin FIG. 10, letting the Young's modulus of silicon be E_(si), theYoung's modulus of polyimide be E_(ph), the secondary moment of thecross section of the silicon part be I_(si), the secondary moment of thecross section of the polyimide part be I_(ph), the moment applied to thesilicon part be M_(si), and the moment applied to the polyimide part beM_(ph), the following relational expression is involved: $\begin{matrix}{\frac{1}{\rho} = {\frac{M_{Si}}{E_{Si} \cdot I_{Si}} = {\frac{M_{Ph}}{E_{Ph} \cdot I_{Ph}} = {k({constant})}}}} & \left\lbrack {{Expression}\quad 8} \right\rbrack\end{matrix}$

 M _(max) =M _(Si) +M _(Ph) ρ:Curvature

Then, the moment of the silicon part, M_(si), and the moment of thepolyimide part, M_(ph), are represented by

M _(Si) =k·E _(Si) ·I _(Si) M _(Ph) =k·E _(Ph) ·I _(Ph)

$k = \frac{M_{Ph}}{E_{Ph} \cdot I_{Ph}}$

Then, the moment applied to the whole of the thermal insulationstructure, M_(max), is $\begin{matrix}{M_{\max} = {{M_{Si} + M_{Ph}} = {{k \cdot E_{Si} \cdot I_{Si}} + M_{Ph}}}} \\{= {{\frac{E_{Si} \cdot I_{Si}}{E_{Ph} \cdot I_{Ph}}M_{Ph}} + M_{Ph}}}\end{matrix}$

Expression 9

The moment of the polyimide part, M_(ph), is$M_{Ph} = \frac{M_{\max}}{\frac{E_{Si} \cdot I_{Si}}{E_{Ph} \cdot I_{Ph}} + 1}$

Likewise, the moment of the silicon part, M_(si), is$M_{Si} = \frac{M_{\max}}{\frac{E_{Ph} \cdot I_{Ph}}{E_{Si} \cdot I_{Si}} + 1}$

The values concerning the silicon part and the polyimide part arecalculated.

Young's modulus of silicon, E _(si),=0.19×10⁻¹² (N/m²)=1.9×10⁻¹²(dyne/cm²)

$\begin{matrix}\begin{matrix}{{E_{Si} = {{1.9 \times 10^{12}\left( {{dyne}\text{/}{cm}^{2}} \right) \times 1.019 \times 10^{- 6}} = {1.93 \times 10^{6}\quad {kgf}\text{/}{cm}^{2}}}}\quad} \\{I_{Si} = {{\frac{1}{12}{bh}^{3}} = {\frac{1}{12} \times 180 \times 3 \times 10^{- 4}({cm}) \times \left( {20 \times 10^{- 4}{cm}} \right)^{3}}}} \\{= {3.6 \times 10^{- 11}\quad {cm}^{4}}}\end{matrix} & \left\lbrack {{Expression}\quad 10} \right\rbrack\end{matrix}$

Therefore, $\begin{matrix}{{E_{si}I_{si}} = {{1.93 \times 106\quad \left( {{kgf}\text{/}{cm}^{2}} \right) \times 3.6 \times 10^{- 11}\quad \left( {cm}^{4} \right)} =}} \\{{{6.94 \times 10^{- 5}\quad \left( {{kgf}\text{/}{cm}^{2}} \right)} = {6.8 \times 10^{- 4}\quad N\quad {{cm}^{2}.}}}}\end{matrix}$

The Young's modulus of polyimide, E_(ph), is 500 MPa $\begin{matrix}\begin{matrix}{E_{Ph} = {{5.0 \times 10^{6}({Pa}) \times 1.019 \times 10^{- 5}} = {5.10 \times 10^{3}\quad {kgf}\text{/}{cm}^{2}}}} \\{I_{Ph} = {{\frac{1}{12}{bh}^{3}} = {\frac{1}{12} \times 30 \times 2 \times 10^{- 4}\quad ({cm}) \times \left( {20 \times 10^{- 4}\quad {cm}} \right)^{3}}}} \\{= {4.0 \times 10^{- 12}\quad {cm}^{4}}}\end{matrix} & \left\lbrack {{Expression}\quad 11} \right\rbrack\end{matrix}$

Therefore, E_(ph) I_(ph)=5.10×10³ (kgf/cm²)×4×10⁻¹² (cm⁴)=2.04×10⁻⁸(kgf/cm²)=2.00×10⁻⁷ (N cm²).

The moment applied to the polyimide part, M_(ph), is as follows:$\begin{matrix}{M_{Ph} = {\frac{1.0 \times 10^{- 5}\left( {{kgf} \cdot {cm}} \right)}{\frac{6.94 \times 10^{- 5}}{2.04 \times 10^{- 8}} + 1} = {2.93 \times 10^{- 9}\quad \left( {{kgf} \cdot {cm}} \right)}}} & \left\lbrack {{Expression}\quad 12} \right\rbrack\end{matrix}$

 M _(ph)=2.93×10⁻⁹ (kgf cm)=2.87×10⁻⁸ (N cm).

Likewise, the moment applied to the silicon part, M_(si), is as follows:$\begin{matrix}{M_{Si} = {\frac{1.0 \times 10^{- 5}\quad \left( {{kgf} \cdot {cm}} \right)}{\frac{2.04 \times 10^{- 6}}{6.94 \times 10^{- 5}} + 1} = {9.99 \times 10^{- 6}\quad \left( {{kgf} \cdot {cm}} \right)}}} & \left\lbrack {{Expression}\quad 13} \right\rbrack\end{matrix}$

 M _(si)=9.99×10⁻⁶ (kgf cm)=9.79×10⁻⁶ (N cm).

Then, the maximum stress applied to the polyimide part, σ_(ph), is asfollows: $\begin{matrix}\begin{matrix}{{Za} = {{\frac{1}{6}{bh}^{2}} = {2.0 \times 10^{- 9}\left( {cm}^{3} \right)}}} \\{\sigma_{Ph} = {\frac{M_{Ph}}{Za} = {\frac{2.93 \times 10^{- 9}\left( {{kgf} \cdot {cm}} \right)}{3.8 \times 10^{- 9}\left( {cm}^{3} \right)} = {{0.77\quad \left( {{kgf}\text{/}{cm}^{2}} \right)} = {7.54 \times 10^{- 2}({MPa})}}}}}\end{matrix} & \left\lbrack {{Expression}\quad 14} \right\rbrack\end{matrix}$

Here, Za is a section modulus. The maximum stress applied to thepolyimide part, σ_(si), is found as follows: $\begin{matrix}{{{Zb} = {{\frac{1}{6}{bh}^{2}} = {3.5 \times 10^{- 8}\left( {cm}^{3} \right)}}}{\sigma_{Si} = {\frac{M_{Si}}{Zb} = {\frac{9.99 \times 10^{- 6}\left( {{kgf} \cdot {cm}} \right)}{3.6 \times 10^{- 8}\left( {cm}^{3} \right)} = {{2.77\left( {{kgf}\text{/}{cm}^{2}} \right)} = {27({MPa})}}}}}} & \left\lbrack {{Expression}\quad 15} \right\rbrack\end{matrix}$

Here, Zb is a section modulus.

Therefore, the stress applied to the thermal insulation area made ofpolyimide becomes about {fraction (1/300)} that in the example shown inFIG. 3. Apparently, it is equivalent to 300 times the strength. In FIG.9, the number of comb teeth formed by the semiconductor substrate 3 andthe flexible area 2 is not limited to that shown in FIG. 9; a similareffect can be produced by providing a structure containing at least twocomb teeth or more.

Second Embodiment

Next, a second embodiment of the invention will be discussed. FIG. 11 isa perspective view of a semiconductor microactuator in the firstembodiment of the invention. FIG. 12A is a sectional view and FIG. 12Bis a top view.

A semiconductor microactuator 1 a of the second embodiment differs fromthe semiconductor microactuator previously described with reference toFIGS. 1 and 2 in that it includes a new thermal insulation area 7Abetween a flexible area 2 and a moving element 5 and that the flexiblearea 2 and the moving element 5 are joined by the thermal insulationarea 7A.

The thermal insulation area 7A is thus provided, whereby the insulationproperties between the flexible area 2 and the moving element 5 areenhanced and heat generated by a diffused resistor 6 is prevented fromescaping to the moving element 5 for efficiently heating the flexiblearea 2, thereby decreasing power consumption.

The rigidity of a thermal insulation area 7 provided between asemiconductor substrate 3 and the flexible area 2 is made different fromthat of the thermal insulation area 7A provided between the flexiblearea 2 and the moving element 5 for determining the displacementdirection of the moving element 5. For example, the rigidity of thethermal insulation area 7 is made higher than that of the thermalinsulation area 7A, whereby the moving element 5 can be displaceddownward in the thickness direction of the semiconductor substrate 3(downward in FIG. 11); the rigidity of the thermal insulation area 7 ismade lower than that of the thermal insulation area 7A, whereby themoving element 5 can be displaced to an opposite side.

In the embodiment, a round for easing a stress applied when the flexiblearea 2 is displaced is provided in the proximity of the joint part ofthe flexible area 2 and the semiconductor substrate 3 or the joint partof the flexible area 2 and the moving part 5.

That is, as shown in FIG. 12B, a projection part 25 projecting inwardroughly from the center of each side of the semiconductor substrate 3which becomes a frame and the flexible area 2 are joined by the thermalinsulation area 7, and a round 25 a is formed so that the shape on thesubstrate face on the semiconductor substrate 3 becomes like R at bothends of the base end part of the projection part 25. A mask is formedand wet etching, etc., is executed, thereby forming the rounds 25 a.

As shown in FIG. 12A, a recess part 27 is made from the lower face sideof the semiconductor substrate 3 in the figure and a thin portion 2Sforming a part of the flexible area 2 is formed in a bottom face part 27a of the recess part 27, and a round 28 is formed so as to become shapedlike R on the boundary between the bottom face part 27 a and a flankpart 27 b of the recess part 27. The recess part 27 is made by etchingfrom the substrate face of the semiconductor substrate. For example, asacrificial layer is formed on the boundary between the bottom face part27 a and the flank part 27 b of the recess part 27 and is removed byetching, whereby isotropy when the sacrificial layer is diffused is usedto form the round 28.

The rounds 25 a and 28 are thus formed, whereby the stress applied whenthe flexible area 2 is displaced is scattered and eased by means of therounds 25 a and 28, preventing the semiconductor substrate 3 from beingdestroyed. That is, if both base end part ends of the projection part 25projecting inward from the semiconductor substrate 3 have an edge, thereis a possibility that the stress of the flexible area 2 will concentrateon the edge, breaking the semiconductor substrate 3. Likewise, if theboundary between the bottom face part 27 a and the flank part 27 b ofthe recess part 27 provided for forming the flexible area 2 has an edge,there is a possibility that the stress of the flexible area 2 willconcentrate on the edge, breaking the semiconductor substrate 3.

FIG. 13 shows another structure example of the semiconductormicroactuator formed with the thermal insulation areas between theflexible area and the semiconductor substrate and between the flexiblearea and the moving element as shown in FIGS. 11 and 12, and amanufacturing method therefor will be discussed.

As shown in FIG. 13, a semiconductor substrate 3 a and a flexible area 2a are joined via a thermal insulation area 7 a and the flexible area 2 aand a moving element 5 a are joined via a thermal insulation area 7 b.The flexible area 2 a is made up of a thin film 2 m and a thin portion 2s different in thermal expansion coefficient, and a diffused resistor 6a is placed on a surface of the thin portion 2 s. Wiring 13 a forsupplying power to the diffused resistor 6 a is connected to thediffused resistor 6 a through the bottom face of the thermal insulationarea 7 a from an electrode pad (not shown) on the semiconductorsubstrate 3 a. Numerals 9 a and 9 b denote protective thin films.

A manufacturing method of the semiconductor microactuator will bediscussed with reference to FIGS. 14A to 14E. First, a silicon oxidefilm 80 a is formed on both faces of a monocrystalline silicon substrate80 by thermal oxidation, etc., and the silicon oxide film 80 a formed onthe rear face of the monocrystalline silicon substrate 80 is etched witha photoresist patterned to a predetermined pattern as a mask, therebyforming an opening 80 b, and the photoresist is removed by plasmaashing, etc. The formed opening 80 b is etched in aqueous potassiumhydroxide (aqueous KOH), etc., thereby forming a gap 80 c (FIG. 14A). Atthis time, TMAH (tetramethyl ammonium hydroxide solution), a hydrazinewater solution, etc., may be used in place of the aqueous KOH. This alsoapplies in the description to follow.

Next, the silicon oxide film 80 a is fully removed, then boron, etc., isdeposited and thermally diffused and diffused resistors 6 a as heatersare formed on the surface of the monocrystalline silicon substrate 80.Subsequently, a silicon oxide film 81 b is formed on both faces of themonocrystalline silicon substrate 80 by thermal oxidation, etc., and asilicon nitride film 81 a is formed on the top of each silicon oxidefilm 81 b by low-pressure CVD (chemical vapor deposition) (FIG. 14B).

The silicon oxide films 81 b and the silicon nitride film 81 a areetched with photoresists patterned to predetermined patterns as masks,thereby forming openings 82, and the photoresists are removed by plasmaashing, etc., (FIG. 14C).

Next, the openings 82 in the monocrystalline semiconductor substrate 80are etched in aqueous KOH, etc., thereby forming a moving element 5 aand thin portions 2 s. At this time, to provide the moving element 5 awith any desired thickness and each thin portion 2 s with any desiredthickness, etching from each face of the monocrystalline semiconductorsubstrate 80 may be started at different timing. Then, themonocrystalline semiconductor substrate 80 is etched, thereby forminggrooves 83 a and 83 b to form thermal insulation areas 7 a and 7 b. Thegrooves 83 a and 83 b are grooves to be filled with an organic materialof polyimide, etc., at a later step, and etching is performed so thatthe bottom thickness of each groove becomes about 10 μm (FIG. 14D).

Subsequently, the substrate surface etched to form the moving element 5a and the thin portions 2 s is oxidized for forming protective films 84required when the substrate is plated (FIG. 14E).

Aluminum is put on the top face of the monocrystalline semiconductorsubstrate 80 by sputtering or EB evaporation and wiring 13 a (aluminumwiring) connected to the diffused resistors 6 a is formed (FIG. 15A).

Next, the grooves 83 a and 83 b are filled with an organic substance 85of polyimide, etc., (FIG. 15B). Thus, a structure wherein the wiring 13a is formed on the lower faces of the organic substances 85 is provided.The organic substances 85 of polyimide, etc., are formed only inpredetermined portions using a semiconductor lithography process.

Next, a metal pattern of a predetermined pattern is formed on thesilicon nitride film 81 a (the protective thin film 9 a in FIG. 13)above the thin portions 2 s by plating, etc., to form thin films 2 m(FIG. 15C). The thin portions 2 s and the thin films 2 m make up abimetal structure of a drive source of the semiconductor microactuator.

Next, etching is performed by RIE, etc., from the rear faces of the thinportions 2 s and the thin portions 2 s are separated from the peripheryof the monocrystalline semiconductor substrate 80 (the semiconductorsubstrate 3 a in FIG. 13) and the moving element 5 a (FIG. 15D), wherebythe moving element 5 a, the flexible areas 2 a, and the semiconductorsubstrate 3 a are thermally insulated and the thermal insulation area 7a, 7 b is provided therebetween.

By the way, in the structure example shown in FIG. 13, the wiring 13 ais placed on the lower part face of the thermal insulation area 7 a, butwiring (aluminum wiring) 13 b may be placed roughly in the middle of thetop and bottom faces of each thermal insulation area 7 a, namely, in thethermal insulation areas 7 a, as shown in FIG. 16.

To thus form the wiring 13 b, after the formation step of the protectivefilm 84 shown in FIG. 14E, the grooves 83 a formed at the step in FIG.14D may be filled with polyimide roughly to the centers at the step offilling with the organic substance 85 of polyimide, etc., shown in FIG.15B, the wiring formation step shown in FIG. 15A may be performed, andthe grooves 83 a may be filled by again executing the filling step shownin FIG. 15B.

Since the wiring 13 b is thus formed in the thermal insulation areas 7a, the aluminum protection effect at an etching step, etc., of latersteps, is produced and a high-reliability wiring structure can beprovided.

In the above-described wiring structure, the wiring may be placed on thetop faces of the thermal insulation areas (FIG. 12A); the wiring isformed on the face on the side where the flexible areas, the thermalinsulation areas, and the semiconductor substrate flush with each other,so that the wiring level difference is lessened and the line breakprevention effect is produced as compared with the case where the wiringis placed in the thermal insulation areas or on the bottom facesthereof.

To thus form the wiring on the top faces of the thermal insulationareas, after the formation step of the protective film 84 shown in FIG.14E, the grooves 83 a formed at the step in FIG. 14D may be filled withpolyimide at the step of filling with the organic substance 85 ofpolyimide, etc., shown in FIG. 15B, then the wiring may be formed on thetop face of polyimide at the wiring formation step shown in FIG. 15A.

Third Embodiment

Next, a third embodiment of the invention will be discussed. FIGS. 17and 18 are a perspective view and a top view to show the structure of asemiconductor microactuator in the third embodiment of the invention. Asemiconductor microactuator in the third embodiment differs from that inthe second embodiment in that the wiring 4 a for supplying power to thediffused resistors 6 is connected to the diffused resistors 6 throughthe tops of the thermal insulation areas 7 in the second embodiment;whereas, in the third embodiment, a fillet part 29 made of an organicmaterial, for example, is formed in a part extending over asemiconductor substrate 3 and a thin portion 2S of a flexible area 2(so-called inlet corner) and wiring 4 a is formed through the filletparts 29. That is, in the embodiment, the wiring 4 a is formed withoutthe intervention of thermal insulation areas 7.

This structure can be manufactured by the following method: A groove isformed from the side of the top face of the semiconductor substratewhere flexible areas 2 are formed, for example, by anisotropic etching,a resin of an organic material, such as polyimide, is poured into thegroove and is cured at a high temperature, and etching is performed forremoval until the fillet parts 29 appear from the rear face of thesemiconductor substrate, then the wiring 4 a is formed on the top facesof the fillet parts 29 by sputtering, etc., aluminum.

The wiring 4 a is made of a material having very good thermalconductivity, such as aluminum, and thus may be heat resistance of afraction of that of thermal insulation area 7 made of a resin althoughit has a small cross-sectional area. If the wiring 4 a is formed in thethermal insulation areas 7, the thermal insulation distance of thewiring 4 a cannot be provided and consequently the thermal insulationperformance of the thermal insulation areas 7 cannot be provided. In theembodiment, the wiring 4 a is formed without the intervention of thethermal insulation areas 7, so that a large thermal insulation distanceof the wiring 4 a can be provided and the thermal insulation effect canbe enhanced with heat resistance degradation suppressed. The mechanicalstrength of the thermal insulation areas 7 is increased as the filletparts 29 are formed.

Thus, with the semiconductor microactuator in the embodiment, thethermal insulation effect is enhanced and further low power consumptionis enabled as compared with the semiconductor microactuator in thesecond embodiment.

Fourth Embodiment

Next, a fourth embodiment of the invention will be discussed. FIGS. 19and 20 are a perspective view and a top view to show the structure of asemiconductor microactuator in the fourth embodiment of the invention. Asemiconductor microactuator 31 in the fourth embodiment differs from thesemiconductor microactuator in the first embodiment in that the fourthin portions 2S each shaped roughly like a quadrangle piece, of theflexible areas 2 are roughly in the shape of a cross with the movingelement 5 at the center in the first embodiment; whereas, in thesemiconductor microactuator 31 of the fourth embodiment, four thinportions 32S of flexible areas 32 are each shaped roughly like L, eachthin portion 32S is connected at one end roughly to the center of eachside of the top face margin opened like a quadrangle, of a movingelement 35, and the flexible areas 32 are shaped like the Buddhist crosswith the moving element 35 at the center. That is, the thin portions 32Sof the flexible areas 32 are placed at equal intervals in everydirection with the moving element 35 at the center. Further, each thinportion 32S is joined at an opposite end to the end of each side of asemiconductor substrate 33 of a quadrangular frame via a thermalinsulation area 37.

Each flexible area 32 is made up of the thin portion 32S and a thin film32M made of aluminum, nickel, etc., like the flexible area in the firstembodiment, and each diffused resistor 36 of heating means is formed onthe surface of the thin portion 32S as in the first embodiment. Externalpower is supplied to the diffused resistors 36 via electrode pads 34placed at the four corners of the semiconductor substrate 33 and wiring34 a. The semiconductor substrate 33, the flexible areas 32, and thethermal insulation area 37 make up a semiconductor device 38.

In the semiconductor microactuator 31, like the semiconductormicroactuator of the first embodiment, as the temperatures of thediffused resistors 36 rise, the flexible areas 32 are heated and aredisplaced downward because of the thermal expansion difference betweeneach thin portion 32S and each thin film 32M (if the thin film 32M has alarger thermal expansion coefficient than the thin portion 32S). Theflexible areas 32 are displaced downward, whereby the moving element 35joined to the flexible areas 32 receives the thermal stress of theflexible areas 32 and is displaced downward with respect to thesemiconductor substrate 33.

In the embodiment, the flexible areas 32 are shaped like the Buddhistcross with the moving element 35 at the center as described above, thusthe displacement of the moving element 35 contains rotation in thehorizontal direction with respect to the semiconductor substrate 33.Since each flexible area 32 is shaped like L, the length of the flexiblearea 32 can be made long as compared with the case where the flexiblearea 32 is shaped simply like a quadrangle piece, and the displacementof the flexible area 32 becomes large, so that displacement of themoving element 35 can be made large. The semiconductor device 38 mayadopt any of the structures shown in FIGS. 3, 6, and 9, and asemiconductor microactuator having similar advantages to those of thesemiconductor microactuators described above can be provided.

Fifth Embodiment

Next, a fifth embodiment of the invention will be discussed. FIGS. 21and 22 are a perspective view and a top view to show the structure of asemiconductor microactuator of the fifth embodiment of the invention. Asemiconductor microactuator 31 a of the embodiment also includesflexible areas 32 shaped like the Buddhist cross with a moving element35 at the center and has thermal expansion areas 37 a each placedbetween the moving element 35 and each flexible area 32 for joining themoving element 35 and the flexible areas 32.

The thermal expansion areas 37 a thus provided, whereby the heatinsulation properties between the flexible areas 32 and the movingelement 35 is enhanced and the heat generated by diffused resistors 36can be prevented from escaping to the moving element 35. Therefore, theflexible areas 32 can be heated efficiently for decreasing powerconsumption as compared with the fourth embodiment.

In the embodiment, a round for easing a stress applied when the flexiblearea 32 is displaced is provided in the proximity of the joint part ofthe flexible area 32 and a semiconductor substrate 33 or the joint partof the flexible area 32 and the moving part 5 as in the embodimentpreviously described with reference to FIGS. 11 and 12. For example, asshown in FIG. 22A, a round 39 a shaped like R is formed at both base endpart ends of a projection part 39 projecting inward from each side endpart of the semiconductor substrate 33.

Sixth Embodiment

Next, a sixth embodiment of the invention will be discussed. FIG. 23 isa perspective view to show the structure of a semiconductormicroactuator of the sixth embodiment of the invention. A semiconductormicroactuator 41 of the embodiment includes a semiconductor substrate 43which becomes a hollow frame shaped roughly like a quadrangle, four thinportions 42S each shaped roughly like a quadrangle piece, the thinportions 42S separated from the semiconductor substrate 43 with one endsjoined via thermal insulation areas 47 inwardly from the sides of thesemiconductor substrate 43, a moving element 45 formed like a hollowquadrangular prismoid with the top face opened like a quadrangle andnarrower toward the bottom, the moving element 45 having top openingmargins connected to opposite ends of the thin portions 42S, and thinfilms 42M of aluminum thin films, nickel thin films, or the like placedon the top faces of the thin portions 42S, each thin film 42M and eachthin portion 42S making up a flexible area 42.

The semiconductor substrate 43, the thin portions 42S, and the movingelement 45 are formed, for example, by working a semiconductor substrateof a silicon substrate, etc. Each thin portion 42S is formed on asurface with an impurity-diffused resistor 46 (diffused resistor 46) ofheating means. Power is supplied to the diffused resistors 46 by wiring44 a connected to electrode pads 44 placed on the semiconductorsubstrate 43 and connected to an external power supply, and thetemperatures of the diffused resistors 46 rise, heating the flexibleareas 42. The thin film 42M is made of aluminum, nickel, or the like asdescribed above and the thin portion 42S is made of silicon, etc.; thethin film 42M and the thin portion 42S have different thermal expansioncoefficients.

Each thermal insulation area 47 for joining the semiconductor substrate43 and the flexible area 42 has roughly the same thickness as the thinportion 42S and is made of a thermal insulation material such as afluoridated resin or polyimide for thermally insulating thesemiconductor substrate 43 and the flexible area 42. The semiconductorsubstrate 43, the flexible areas 42, and the thermal insulation areas 47each between the semiconductor substrate 43 and the flexible area 42make up a semiconductor device 48. The semiconductor microactuator 41has a cantilever structure with each flexible area 42 supported at oneend on the semiconductor substrate 43.

In the semiconductor microactuator 41, upon application of power to thediffused resistors 46, the temperature rises, heating the flexible areas42, and a thermal stress occurs because of the difference between thethermal expansion coefficients of the thin film 42M and the thin portion42S making up each flexible area 42. For example, if metal thin films ofaluminum, nickel, etc., are formed as the thin films 42M, the metal ofaluminum, nickel, etc., has a lager thermal expansion coefficient thansilicon forming the thin portions 42S, so that the flexible areas 42 arebent downward in the figure. The moving element 45 placed contiguouswith the flexible areas 42 receives the thermal stress of the flexibleareas 42 and is displaced downward with respect to the semiconductorsubstrate 43.

In the embodiment, the flexible areas 42 are of cantilever structure, sothat large flexibility of the flexible areas 42 can be provided anddisplacement of the flexible areas 42 at the heating time becomes large.Thus, displacement of the moving element 45 becomes large and a largeforce is provided. The semiconductor device 48 may adopt any of thestructures previously described with reference to FIGS. 3, 6, and 9 inthe first embodiment, and a semiconductor microactuator having similaradvantages to those of the semiconductor microactuators described abovecan be provided.

Seventh Embodiment

Next, a seventh embodiment of the invention will be discussed. FIG. 24is a perspective view to show the structure of a semiconductormicroactuator 41 a of the seventh embodiment of the invention. Theseventh embodiment differs from the sixth embodiment in that eachflexible area 42 and a moving element 45 are joined by a thermalinsulation area 47 a made of a resin such as polyimide or a fluoridatedresin, the thermal insulation area 47 a being placed between theflexible area 42 and the moving element 45.

The new thermal insulation area 47 a is thus provided, whereby theinsulation properties between the flexible area 42 and the movingelement 45 are enhanced and heat generated by a diffused resistor 46 canbe prevented from escaping to the moving element 45; the flexible areas42 can be heated efficiently for decreasing power consumption ascompared with the sixth embodiment.

Eighth Embodiment

Next, an eighth embodiment of the invention will be discussed. FIG. 25is a perspective view to show the structure of a semiconductormicroactuator 41 b of the eighth embodiment of the invention. The eighthembodiment differs from the seventh embodiment in that a thin film 47Mof a flexible area 42 and a thermal insulation area 47 are made of thesame material, a resin having thermal insulation properties, such aspolyimide or a fluoridated resin, whereby it is made possible to formthe thermal insulation area 47 and the thin film 47M at the same time;the manufacturing process can be simplified.

A moving element 45 of the semiconductor microactuator 41 b is formedwith a concave part 45H as a groove made from the top face. The heatcapacity of the moving element 45 lessens as compared with a movingelement 45 a of a semiconductor microactuator 41 c shown in FIG. 26 (themoving element 45 a formed with no concave part), so that thetemperatures of the flexible areas 42 can be raised rapidly. The concavepart 45H is formed, whereby the weight (volume) of the moving elementlessens, so that the semiconductor microactuator 41 b also has theadvantage that it does not malfunction upon reception of an externalshock.

Ninth Embodiment

Next, a ninth embodiment of the invention will be discussed. FIG. 27 isa partially cutaway view in perspective of the structure of asemiconductor microvalve 55 in the ninth embodiment of the invention.The semiconductor microvalve 55 includes a pedestal 50 of a fluidelement formed by working a substrate and an actuator section joinedonto the top of the pedestal 50 by anodic junction or eutectic junction.The semiconductor microactuator 1 comprising the flexible areas 2 in theshape of a cross with the moving element 5 at the center previouslydescribed with reference to FIGS. 1 and 2 is used as the actuatorsection.

The pedestal 50 is formed with a through hole 51 (so-called orifice)corresponding to a fluid flow passage at the position corresponding tothe moving element 5 of the semiconductor microactuator 1 placed on thesurface of the pedestal 50, and a bed part 52 with a roughly flat topface, projecting from the surroundings is formed in the periphery of atop face opening of the through hole 51. The moving element 5corresponds to a so-called valve body.

In the described semiconductor microvalve 55, when power is supplied tothe diffused resistors 6 for heating the flexible areas 2, each flexiblearea 2 is displaced because of the thermal expansion difference betweenthe thin portion 2S and the thin film 2M and the moving element 5 joinedto the flexible areas 2 is displaced. As the moving element 5 isdisplaced, the spacing between the bottom face part of the movingelement 5 and the bed part 52 of the pedestal 51 changes, controllingthe quantity of the fluid flowing through the through hole 51.

The semiconductor microvalve 55 of the embodiment is also formed withthe thermal insulation area 7 made of a resin of polyimide, etc.,between the semiconductor substrate 3 and each flexible area 2, so thatthe heat for heating the flexible areas 2 can be prevented from escapingto the semiconductor substrate 3. Thus, it is made possible to suppresspower consumption in driving the semiconductor microvalve.

Since the four flexible areas 2 are in the shape of a cross with themoving element 5 at the center, the semiconductor microvalve is providedwith good control accuracy of the moving element 5 and fluid.

FIG. 28 shows a configuration example of using the semiconductormicroactuator 1 a previously described with reference to FIGS. 11 and 12as the actuator section of the semiconductor microvalve in FIG. 27. Thesemiconductor microvalve in FIG. 28 includes the pedestal 50 and thesemiconductor microactuator 1 a joined via spacer layers 53 made ofpolyimide.

The thermal insulation area 7A is also provided between each flexiblearea 2 and the moving element 5, so that it is made possible to morelessen the escape heat from the flexible areas 2 as compared with thesemiconductor microvalve shown in FIG. 27, and power consumption indriving the semiconductor microvalve can be suppressed.

The advantage provided by providing rounds each for easing a stressapplied when the flexible area 2 is displaced in the joint part of theflexible area 2 and the semiconductor substrate 3 or in the proximity ofthe joint part of the flexible area 2 and the moving part 5 is similarto that previously described with reference to FIGS. 11 and 12.

Further, the spacer layers 53 are formed between the pedestal 50 and thesemiconductor microactuator 1 a, whereby the following advantage isprovided: Normally, the semiconductor microactuator 1 a is made of asilicon substrate and the pedestal 50 is made of a glass substrate.Since both are joined under a high temperature (anodically joined at400° C.), a stress occurs therebetween at a room temperature because ofthe shrinkage degree difference caused by the thermal expansiondifference between the silicon and glass substrates. Since the stressconcentrates on the flexible areas 2 of the semiconductor microactuator1 a, sufficient displacement of the flexible areas 2 cannot be providedand the drivability of the semiconductor microvalve worsens. Then, thespacer layers 53 are provided between the pedestal 50 and thesemiconductor microactuator 1 a, whereby the stress occurringtherebetween can be absorbed and eased as described above.

The operation of the semiconductor microvalve in FIG. 28 is similar tothat of the semiconductor microvalve in FIG. 27 and therefore will notbe discussed again.

FIG. 29 shows a configuration example of using the semiconductormicroactuator 1 b previously described with reference to FIG. 17 as theactuator section of the semiconductor microvalve in FIG. 27. Thesemiconductor microvalve in FIG. 29 differs from that shown in FIG. 28in that the wiring 4 a for supplying power to the diffused resistors 6for heating the flexible areas 2 is formed without the intervention ofthe thermal insulation areas 7. Since it is made possible to provide alarge thermal insulation distance of the wiring 4 a, the semiconductormicrovalve can be provided with a higher thermal insulation effect andpower consumption for driving the semiconductor microvalve can besuppressed.

The operation of the semiconductor microvalve in FIG. 29 is similar tothat of the semiconductor microvalve in FIG. 27 and therefore will notbe discussed again.

Tenth Embodiment

Next, a tenth embodiment of the invention will be discussed. FIG. 30 isa partially cutaway view in perspective of the structure of asemiconductor microvalve in the tenth embodiment of the invention. Thesemiconductor microvalve includes a pedestal 56 of a fluid elementformed by working a substrate and an actuator section joined onto thetop of the pedestal 56 by anodic junction or eutectic junction. Thesemiconductor microactuator 31 comprising the flexible areas 32 shapedlike the Buddhist cross with the moving element 35 at the centerpreviously described with reference to FIGS. 19 and 20 is used as theactuator section.

The pedestal 56 is formed with a through hole 57 (so-called orifice)corresponding to a fluid flow passage at the position corresponding tothe moving element 35 of the semiconductor microactuator 31 placed onthe surface of the pedestal 56, and a bed part 58 with a roughly flattop face, projecting from the surroundings is formed in the periphery ofa top face opening of the through hole 57. The moving element 35corresponds to a so-called valve body.

In the described semiconductor microvalve, when power is supplied to thediffused resistors 36 for heating the flexible areas 32, each flexiblearea 32 is displaced because of the thermal expansion difference betweenthe thin portion 32S and the thin film 32M and the moving element 35joined to the flexible areas 32 is displaced. As the moving element 35is displaced, the spacing between the bottom face part of the movingelement 35 and the bed part 58 of the pedestal 56 changes, controllingthe quantity of the fluid flowing through the through hole 57.

The semiconductor microvalve of the embodiment is also formed with thethermal insulation area 37 made of a resin of polyimide, etc., betweenthe semiconductor substrate 33 and each flexible area 32, so that theheat for heating the flexible areas 32 can be prevented from escaping tothe semiconductor substrate 33. Thus, it is made possible to suppresspower consumption in driving the semiconductor microvalve.

Since the semiconductor microvalve of the embodiment includes theflexible areas 32 each shaped like L, the length of each flexible areais long, so that displacement of the flexible areas 32 becomes large,thus displacement of the moving element 35 can be made large. Therefore,the semiconductor microvalve is provided with a wide range of fluid flowquantity control.

FIG. 31 shows a configuration example of using the semiconductormicroactuator 31 a previously described with reference to FIGS. 21 and22 as the actuator section in FIG. 30. The semiconductor microvalve inFIG. 31 also includes the thermal insulation area 37 a provided betweeneach flexible area 32 and the moving element 35, so that it is madepossible to more lessen the escape heat from the flexible areas 32 ascompared with the semiconductor microvalve shown in FIG. 30, and powerconsumption in driving the semiconductor microvalve can be suppressed.

The advantage provided by providing rounds each for easing a stressapplied when the flexible area 32 is displaced in the proximity of thejoint part of the flexible area 32 and the semiconductor substrate 33 orthe joint part of the flexible area 32 and the moving part 35 is similarto that previously described with reference to FIGS. 21 and 22.

Eleventh Embodiment

Next, an eleventh embodiment of the invention will be discussed. FIG. 32is a partially cutaway view in perspective of the structure of asemiconductor microrelay in the eleventh embodiment of the invention.The semiconductor microrelay in FIG. 32 includes a fixed piece 65 of afixed element formed on a surface with fixed contacts 67 and 68 and anactuator section joined onto the top of the fixed piece 65 by anodicjunction or eutectic junction. The semiconductor microactuator 41previously described with reference to FIG. 23 is used as the actuatorsection.

A moving contact 66 is provided on the bottom face of the moving element45 of the semiconductor microactuator 41, and the fixed contacts 67 and68 on the fixed piece 65 are placed at the positions corresponding tothe moving contact 66 away therefrom so that they can come in contactwith the moving contact 66.

When an electric current flows into the diffused resistors 46 and theflexible areas 42 are heated, each flexible area 42 is displaced becauseof the thermal expansion difference between the thin portion 42S and thethin film 42M and the moving element 45 is displaced. As the movingelement 45 is displaced, the moving contact 66 provided on the bottomface of the moving element 45 comes in contact with the fixed contacts67 and 68, and the fixed contacts 67 and 68 are brought into conductionthrough the fixed contact 66, turning on the relay.

The actuator section of the semiconductor microrelay of the embodimentuses the semiconductor microactuator 41; the semiconductor microrelay isprovided with a high thermal insulation effect between the flexibleareas 42 and the semiconductor substrate 43 and small power consumptionas described in the sixth embodiment. The semiconductor microactuator 41is of a cantilever structure with the semiconductor substrate 43 as afixed end and the semiconductor microrelay is provided with a largecontact pressure.

Twelfth Embodiment

Next a twelfth embodiment of the invention will be discussed. FIG. 33 isa perspective view to show the structure of a semiconductor microrelayin the twelfth embodiment of the invention. The actuator section shownin FIG. 32 uses the semiconductor microactuator 41 b previouslydescribed with reference to FIG. 25.

That is, in the semiconductor microrelay of the embodiment, the thinfilms 47M of the flexible areas 42 and the thermal insulation areas 47for joining the flexible areas 42 and the semiconductor substrate 43 aremade of the same material, such as polyimide.

In the semiconductor microrelay shown in FIG. 33, the moving element 45is formed with the concave part 45H. As compared with a moving elementformed with no concave part shown in FIG. 37, the small heat capacity issmall and the temperatures of the flexible areas 42 can be raisedrapidly, and the weight (volume) of the moving element lessens, thus themoving element does not malfunction upon reception of an external shock,as previously described with reference to FIG. 25.

Next, a semiconductor microrelay manufacturing method in the embodimentwill be discussed. A semiconductor substrate 43, such as a siliconsubstrate, (see FIG. 34A) is etched for removal from the bottom facewith KOH, etc., with a silicon nitride film, etc., as a mask, forming agap 40 (see FIG. 34B). The gap 40 becomes a contact gap between movingand fixed contacts in the semiconductor microrelay. The semiconductorsubstrate 43 of a silicon substrate may be the p or n type andpreferably the crystal orientation is <100>.

Next, a diffused resistor 46 is formed on the top face of thesemiconductor substrate 43 by ion implantation or impurity diffusion(see FIG. 34C). The impurities may be the p or n type.

Further, a silicon nitride film, etc., is formed on both faces of thesemiconductor substrate 43 and patterning is performed. Then, etching(anisotropic etching) is executed for removal with KOH, etc., from thetop face of the semiconductor substrate 43 and a concave part 45H isformed on the top of a moving element 45 as a hollow shape. At the sametime, etching (anisotropic etching) is executed for removal with KOH,etc., from the bottom face of the semiconductor substrate 43 to make aconcave part, and the bottom face portion of the concave part is formedas a thin portion 42S forming a part of a flexible area (see FIG. 34D).

Next, etching is executed for removal with a silicon nitride film, etc.,as a mask from the top face of the semiconductor substrate 43 to makeholes 47B and 47C in the portions which will become thermal insulationareas 47 and 47 a (see FIG. 35A). The etching depth corresponds to thethickness of the thermal insulation area 47, 47 a.

At the next step, an aluminum thin film is formed by sputtering, etc.,and patterning is performed, whereby wiring 49A for supplying power tothe diffused resistor 46 and the like are formed (see FIG. 35B).

Next, the full face of the semiconductor substrate 43 is coated with afilm of thermal insulation material of polyimide, etc., to fill in theholes 47B and 47C. Then, the thermal insulation material except that ofthe fill-in portions or that above the thin portion 42S is removed byetching, etc., and the thermal insulation areas 47 and 47 a and a thinfilm 47M are formed of the same material of polyimide, etc., (see FIG.35C). The bottom face sides of the thermal insulation areas 47 and 47 aare etched for removal (see FIG. 35D) and the moving element 45 isformed on the bottom face side with a moving contact 66 (describedlater) made of gold cobalt, etc., by plating, etc., (see FIG. 35E).

Then, the semiconductor substrate 43 thus worked and a fixed piece 65formed with a fixed contact 67 of gold cobalt, etc., by plating arejoined by anodic junction, etc., (see FIG. 36A). Last, the movingelement 45 and the flexible area 42 are separated from the semiconductorsubstrate 43 which becomes a frame by RIE, etc., for manufacturing asemiconductor microrelay (see FIG. 36B). That is, the semiconductormicroactuator 41 b is manufactured.

Since the thin film 47M of the flexible area 42 and the thermalinsulation area 47 are thus formed of the same material at the sametime, so that the manufacturing process is simplified and the costs canbe reduced.

FIG. 38 shows a so-called bimetal structure consisting of the thinportion 42S and the thin film 47M of the flexible area 42 in thesemiconductor microrelay of the embodiment. As shown in the figure,polyimide (trade name “Photonis”) 20 μm thick as the thin film 47M isformed on the top of the thin portion 42S made of silicon 10 μm thick.The flexible area 42 has plane dimensions of 1000 μm×1000 μm. At thistime, the bend of the flexible area 42 is represented by the followingTimochenko's expression: $\begin{matrix}\begin{matrix}{\frac{1}{\rho} = \frac{6\left( {\alpha_{Si} - \alpha_{ph}} \right)\Delta \quad {T\left( {t_{Si} + t_{ph}} \right)}{t_{Si} \cdot t_{ph} \cdot E_{Si} \cdot E_{ph}}}{{3\left( {t_{Si} + t_{ph}} \right)^{2}t_{Si}t_{ph}E_{Si}E_{ph}} + {\left( {{t_{Si}E_{Si}} + {t_{ph}E_{ph}}} \right)\left( {{t_{Si}^{3}E_{Si}} + {t_{ph}^{3}E_{ph}}} \right)}}} \\{{w = {2\rho \quad {\sin^{2}\left( \frac{L}{2\rho} \right)}}};\quad {{\frac{L}{2\rho}\lbrack{rad}\rbrack}\quad {{in}\quad\lbrack{rad}\rbrack}\quad {units}}}\end{matrix} & \left\lbrack {{Expression}\quad 16} \right\rbrack\end{matrix}$

where ΔT denotes temperature change.

FIG. 39 shows the calculation result of the expression to which specificnumeric values are assigned. As shown in FIG. 39, the higher thetemperature of the flexible area 42, the larger the displacement (bend)of the flexible area 42. If the bend becomes larger than the contact gapbetween the moving contact 66 and the fixed contact 67, 68 of thesemiconductor microrelay, the moving contact 66 comes in contact withthe fixed contacts 67 and 68, turning on the relay.

The bimetal operation when the contact gap is 20 μm and the bimetal isat 200° C. will be discussed. As shown in FIG. 39, displacement of thebimetal at 200° C. is about 65 μm.

The semiconductor microrelay is of a cantilever structure and the beamcorresponding to the flexible area 42 is displaced as shown in FIG. 40.Displacement of the tip, Xa, is represented as Xa=(Fa τa³)/(3Ea Ia). Fadenotes the force applied to the tip of the beam, ta denotes thethickness of the beam, τa denotes the length of the beam, and Ea denotesthe Young's modulus of the beam. Ia denotes the secondary moment of thecross section of the beam. If the beam is rectangular in cross section,Ia=ba ta³/12 (where ba denotes the deep width of the beam), thus thebend of the tip, Xa,=4 Fa τa³/(ba ta³ Ea). According to this expression,the force applied to the tip of the beam, Fa, is represented as Fa=(Xaba ta³ Ea)/(4 τa³). Letting the contact gap be 20 μm, contact pressurefa becomes equal to ((Xa−20 μm) ba ta³ Ea)/(4 τa³). Since the bend ofthe tip, Xa, is 65 μm, the contact pressure fa becomes equal to 0.87gf=8.5×10⁻³ N; the contact pressure almost close to 1 gf (9.8×10⁻³ N) isprovided.

Thirteenth Embodiment

Next, a thirteenth embodiment of the invention will be discussed. FIG.41 is a perspective view to show the structure of a semiconductormicrorelay of the thirteenth embodiment of the invention. Thesemiconductor microrelay shown in FIG. 41 includes the semiconductormicroactuator 41 previously described with reference to FIG. 23 as theactuator section of the semiconductor microrelay shown in FIG. 33. Thesemiconductor microrelay of the embodiment differs from thesemiconductor microrelay in FIG. 33 in that the thin film 42M of eachflexible area 42 is made of a metal thin film such as an aluminum ornickel thin film.

Also in the semiconductor microrelay of the embodiment, the movingelement 45 is formed with the concave part 45H; as compared with asemiconductor microrelay shown in FIG. 48 with a moving element formedwith no concave part, the temperatures of the flexible areas 42 can beraised rapidly, and the weight (volume) of the moving element lessens,thus malfunction can be prevented upon reception of an external shock,as in the twelfth embodiment.

Next, manufacturing methods of the semiconductor microrelay shown inFIG. 41 will be discussed. First, a manufacturing method of thesemiconductor microrelay wherein the thin film 42M forming a part ofeach flexible area 42 is made of an aluminum thin film will bediscussed.

A semiconductor substrate 43, such as a silicon substrate, (see FIG.42A) is etched for removal from the bottom face with KOH, etc., with asilicon nitride film, etc., as a mask, forming a gap 40 (see FIG. 42B).The gap 40 becomes a contact gap between moving and fixed contacts inthe semiconductor microrelay. The semiconductor substrate 43 (siliconsubstrate) may be the p or n type and preferably the crystal orientationis <100>.

Next, a diffused resistor 46 is formed on the top face of thesemiconductor substrate 43 by ion implantation or impurity diffusion(see FIG. 42C). The impurities may be the p or n type.

Further, a silicon nitride film, etc., is formed on both faces of thesemiconductor substrate 43 and patterning is performed. Then, etching(anisotropic etching) is executed for removal with KOH, etc., from thetop face of the semiconductor substrate 43 and a concave part 45H isformed on the top of a moving element 45 as a hollow shape. At the sametime, etching (anisotropic etching) is executed for removal with KOH,etc., from the bottom face of the semiconductor substrate 43 to make aconcave part, and the bottom face portion of the concave part is formedas a thin portion 42S forming a part of a flexible area (see FIG. 42D).

Next, etching is executed for removal with a silicon nitride film, etc.,as a mask from the top face of the semiconductor substrate 43 to makeholes 47B and 47C in the portions which will become thermal insulationareas 47 and 47 a (see FIG. 43A). The etching depth corresponds to thethickness of the thermal insulation area 47, 47 a.

At the next step, an aluminum thin film is formed by sputtering, etc.,and patterning is performed, whereby a thin film 42M forming a part of aflexible area and wiring 49A for supplying power to the diffusedresistor 46 are formed, as shown in FIG. 43B. Then, the full face of thesemiconductor substrate 43 is coated with a film of thermal insulationmaterial of polyimide, etc., to fill in the holes 47B and 47C made inthe top face of the semiconductor substrate 43, and the thermalinsulation material other than the fill-in portions is removed byetching, etc., and the thermal insulation areas 47 and 47 a are formed(see FIG. 43c).

Then, the bottom face sides of the thermal insulation areas 47 and 47 aare etched for removal for forming the thermal insulation areas 47 and47 a the thermal insulation areas 47 and 47 a made of only the thermalinsulation material (see FIG. 43D). Next, the moving element 45 isformed on the bottom face side with a moving contact 66 made of goldcobalt, etc., by plating, etc.

Next, the semiconductor substrate 43 thus worked and a fixed piece 65formed with a fixed contact 67 of gold cobalt, etc., by plating arejoined by anodic junction, etc., (see FIG. 44A). Last, the movingelement 45 and the flexible area 42 are separated from the semiconductorsubstrate 43 which becomes a frame by RIE, etc., for manufacturing asemiconductor microrelay. That is, the semiconductor microactuator 41 ais manufactured.

Next, a manufacturing method of the semiconductor microrelay shown inFIG. 41 wherein the thin film 42M is made of nickel will be discussed.As shown in FIGS. 45A to 45E, the step of forming a gap 40 in the bottomface of a semiconductor substrate 43, the step of forming a diffusedresistor 46 in the top face of the semiconductor substrate 43, the stepof forming a concave part 45H on the top of a moving element 45, thestep of forming a thin portion 42S of a flexible area 42, and the stepof making holes 47B and 47C of portions which will become thermalinsulation areas are similar to the steps previously described withreference to FIGS. 42A to 42D and 43A and therefore will not bediscussed again.

At the next step, an aluminum thin film is formed by sputtering, etc.,and patterning is performed, whereby wiring 49A for supplying power tothe diffused resistor 46 and the like are formed, as shown in FIG. 46A.Next, the full face of the semiconductor substrate 43 is coated with afilm of thermal insulation material of polyimide, etc., to fill in theholes 47B and 47C made in the top face of the semiconductor substrate43, the thermal insulation material other than the fill-in portions isremoved by etching, etc., and the thermal insulation areas 47 and 47 aare formed, as shown in FIG. 46B.

Then, the bottom face sides of the thermal insulation areas 47 and 47 aare etched for removal (see FIG. 46C), the thin portion 42S is formed onthe top face with a nickel thin film as thin film 42M by plating, etc.,(see FIG. 46D), and the moving element 45 is formed on the bottom faceside with a moving contact 66 made of gold cobalt, etc., by plating,etc., (see FIG. 46E).

Next, the semiconductor substrate 43 thus worked and a fixed piece 65formed with a fixed contact 67 of gold cobalt, etc., by plating arejoined by anodic junction, etc., (see FIG. 47A). Last, the movingelement 45 and the flexible area 42 are separated from the semiconductorsubstrate 43 which becomes a frame by RIE, etc., for manufacturing asemiconductor microrelay (see FIG. 47B). That is, the semiconductormicroactuator 41 a is manufactured.

FIG. 49 shows a so-called bimetal structure consisting of the thinportion 42S and the thin film 42M of the flexible area 42 in thesemiconductor microrelay shown in FIG. 41. As shown in FIG. 49, analuminum thin film 5 μm thick as the thin film 42M is formed on the topof the thin portion 42S made of silicon 15 μm thick. The flexible area42 has plane dimensions of 1000 μm×1000 μm.

At this time, the displacement (bend) of the flexible area 42 isrepresented by the following Timochenko's expression: $\begin{matrix}\begin{matrix}{\frac{1}{\rho} = \frac{6\left( {\alpha_{Si} - \alpha_{Al}} \right)\Delta \quad {T\left( {t_{Si} + t_{Al}} \right)}{t_{Si} \cdot t_{Al} \cdot E_{Si} \cdot E_{Al}}}{{3\left( {t_{Si} + t_{Al}} \right)^{2}t_{Si}t_{Al}E_{Si}E_{Al}} + {\left( {{t_{Si}E_{Si}} + {t_{Al}E_{Al}}} \right)\left( {{t_{Si}^{3}E_{Si}} + {t_{Al}^{3}E_{Al}}} \right)}}} \\{{W = {2\rho \quad {\sin^{2}\left( \frac{L}{2\rho} \right)}}};{\frac{L}{2\rho}\quad {{in}\quad\lbrack{rad}\rbrack}\quad {units}}}\end{matrix} & {\left\lbrack {{Expresssion}\quad 17} \right\rbrack \quad}\end{matrix}$

where ΔT denotes temperature change.

FIG. 50 shows the calculation result of the expression to which specificnumeric values are assigned. As shown in FIG. 50, the higher thetemperature of the flexible area 42, the larger the displacement (bend)of the flexible area 42. If the displacement becomes larger than thecontact gap between the moving contact 66 and the fixed contact 67, 68of the semiconductor microrelay, the moving contact 66 comes in contactwith the fixed contacts 67 and 68, turning on the relay.

The bimetal operation when the contact gap is 20 μm and the flexiblearea 42 is at 200° C. will be discussed. As shown in FIG. 50,displacement of the flexible area 42 at 200° C. is about 70 μm.

The contact pressure fa is represented as fa=((Xa−20 μm) ba ta³ Ea)/(4τa³), as described above. If the contact pressure fa is found, fa=0.82gf=8.0×10⁻³ N; the contact pressure almost close to 1 gf (9.8×10⁻³ N) isprovided.

On the other hand, to use a nickel thin film as the thin film 42M,nickel has a smaller thermal expansion coefficient than aluminum, thusthe displacement (bend) of the flexible area 42 in response totemperature change is small. However, nickel has a larger Young'smodulus than aluminum, so that a large thermal stress can be generated.

FIG. 51 shows the displacement characteristics of the flexible area 42with the thin film 42M made of aluminum and that with the thin film 42Mmade of nickel as the thickness of the thin portion 42S made of siliconis changed, wherein the aluminum film and the nickel film are each 5 μmthick and the temperature of the flexible area 42 is 200° C. As seen inthe figure, when the thin portion 42S is 20 μm thick, thecharacteristics of the flexible area 42 with aluminum and that withnickel are inverted and when the thin portion 42S becomes more than 20μm thick, the displacement characteristic of the flexible area 42 withthe thin film 42M made of nickel becomes larger than that with the thinfilm 42M made of aluminum. Thus, if the thin portion 42S is thick, agood characteristic can be provided by using nickel as the thin film42M.

FIG. 52 shows another configuration example of the semiconductormicrorelay in the embodiment. The semiconductor microrelay in FIG. 52differs from that in FIG. 41 in that it includes the fixed piece 65 andthe semiconductor microactuator 41 a joined via a spacer layer 63 madeof polyimide (for example, anodic junction). The stress occurringbetween the fixed piece 65 and the semiconductor microactuator 41 a canbe absorbed and eased, as in the embodiment previously described withreference to FIG. 28.

FIGS. 57 and 58 show another configuration example of the semiconductormicroactuator. FIG. 58(a) is a sectional view and FIG. 58(b) is a topview. A semiconductor microactuator 7 shown in these figures is definedby the semiconductor substrate 3, made of the silicon or the like, whichbecomes a hollow parallelepiped shaped frame and a moving element 1,made of the silicon or the like, jointed at four portions throughsuspending means 4 from an inner side of the semiconductor substrate tosuspend the moving element 1 from the semiconductor substrate 3.

The moving element 1 is shaped in a hollow truncated right pyramid insuch a manner that quadrangle shaped portion is gradually reduced in anarea along with a downwardly direction. A boss 2 is defined by the lowerquadrangle portion of the truncated right pyramid. The boss 2 issuspended by cantilevered beam 6 in such a manner that each cantileveredbeam extends in a downwardly direction from one side of upper quadrangleof the truncated right pyramid. Each cantilevered beam 6 of four themserves as the extended leg portion of the crosswise through the boss 2.The suspending means 4 is made of polyimide, fluoridated resin or thelike and is formed in such a manner that the surface of thesemiconductor substrate 3 is jointed to the suspending means 4 contactedoverlappingly to the upper side of the cantilevered beam 6 to join thesemiconductor substrate 3 and the moving element 1. The cantileveredbeam 6 is provided with heating means 5, made of the diffusion resistoror the like, for heating the cantilevered beam 6.

FIGS. 59 and 60 show another configuration example of the semiconductormicroactuator. FIG. 59 is a partinally cut away view in perspective ofthe structure of a semiconductor microactuator using semiconductordevice of the present invention. FIG. 60 is a top view. A semiconductormicroactuator 10 shown in these figures is defined by the semiconductorsubstrate 13, made of the silicon or the like, which becomes a hollowparallelepiped shaped frame and a moving element 11, made of the siliconor the like, jointed at four portions through suspending means 14 froman inner side of the semiconductor substrate to suspend the movingelement 11 from the semiconductor substrate 13.

The moving element 11 is shaped in a hollow truncated right pyramid insuch a manner that quadrangle shaped portion is gradually reduced in anarea along with a downwardly direction. A boss 12 is defined by thelower quadrangle portion of the truncated right pyramid. The boss 12 issuspended by cantilevered beam 16 in such a manner that eachcantilevered beam extends in a downwardly direction from one side ofupper quadrangle of the truncated right pyramid. Each cantilevered beam16 of four them serves as the extended leg portion of the gammadionthrough the boss 12. The suspending means 4 is made of polyimide,fluoridated resin or the like and is formed in such a manner that thesurface of the semiconductor substrate 13 is jointed to the suspendingmeans 14 contacted overlappingly to the upper side of the cantileveredbeam 16 to join the semiconductor substrate 13 and the moving element11.

FIG. 61 shows another configuration example of the semiconductormicrovalve, and is a partinally cut away view in perspective of thestructure of a semiconductor microvalve using semiconductor device ofthe present invention. A semiconductor microvalve 30 is defined by avalve mount 31 serving as a fluid control element and a valve body 32joined to the upper portion of the valve mount 31 through anodicjunction or eutectic junction. This valve body employs the structure assame as the microactuator as shown in FIGS. 57 and 58.

A orifice 35 is provided on the surface of the valve mount 31 to beconfronted with a boss 2 of the valve body 32, and serves as a holeportion corresponding to the fluid flow path. A mount portion 36 with anupper flat surface is formed by projecting a portion vicinity of theorifice 35 to surround the orifice 35.

At that time, a current flows to the heating means 5 to deform the beamof the moving element 1 so as to actuate the moving element 1. Anactuation of the moving element 1 changes the gap defined by the bottomsurface of the boss 2 of the valve body 41 and the mount portion 36 tocontrol a flow amount passing through the orifice 35.

FIG. 62 shows another configuration example of the semiconductormicrovalve, and is a partinally cut away view in perspective of thestructure of a semiconductor microvalve using semiconductor device ofthe present invention. A semiconductor microvalve is defined by a valvemount 41 serving as a fluid control element and a valve body 42 joinedto the upper portion of the valve mount 41 through anodic junction oreutectic junction. This valve body employs the structure as same as themicroactuator 10 as shown in FIGS. 59 and 60.

A orifice 45 is provided on the surface of the valve mount 41 to beconfronted with a boss 12 of the valve body 42, and serves as a holeportion corresponding to the fluid flow path. A mount portion 46 with anupper flat surface is formed by projecting a portion vicinity of theorifice 45 to surround the orifice 45.

At that time, a current flows to the heating means (not shown inFigures) to deform the beam 16 of the moving element 11 so as to actuatethe moving element 11. An actuation of the moving element 1 changes thegap defined by the bottom surface of the boss 12 of the valve body 41and the mount portion 46 to control a flow amount passing through theorifice 45.

As described above, the semiconductor microactuator using thesemiconductor device, the semiconductor microvalve, and thesemiconductor microrelay in the related arts require large powerconsumption and thus it becomes difficult to drive them with a batteryand it is made impossible to miniaturize them for portable use.

It is therefore an object of the invention to provide a semiconductordevice with small power consumption, manufactured by an easymanufacturing process, a semiconductor microactuator using thesemiconductor device, a semiconductor microvalve, a semiconductormicrorelay, and a semiconductor microactuator manufacturing method.

Means for Solving the Problem

To the end, according to a first aspect of the present invention, thereis provided a semiconductor device comprising a semiconductor substrate,a flexible area being isolated from the semiconductor substrate anddisplaced in response to temperature change, and a thermal insulationarea being placed between the semiconductor substrate and the flexiblearea and made of a resin for joining the semiconductor substrate and theflexible area. The thermal insulation area made of a resin is placedbetween the semiconductor substrate and the flexible area, whereby heatescape when the temperature of the flexible area is changed isprevented, so that power consumption can be suppressed and further themanufacturing method is simple.

In a second aspect to the present invention, in the semiconductor deviceas first aspect of the present invention, the material of which thethermal insulation area is made has a thermal conductivity coefficientof about 0.4 W/(m° C.) or less. The heat insulation properties betweenthe flexible area and the semiconductor substrate are enhanced.

In a third aspect of the present invention, in the semiconductor deviceas the second aspect of the present invention, the material of which thethermal insulation area is made is polyimide. The heat insulationproperties between the flexible area and the semiconductor substrate areenhanced and manufacturing the semiconductor device is facilitated.

In a fourth aspect of the present invention, in the third aspect of thepresent invention, the material of which the thermal insulation area ismade is a fluoridated resin. The heat insulation properties between theflexible area and the semiconductor substrate are enhanced andmanufacturing the semiconductor device is facilitated.

In a fifth aspect of the present invention, in the first to fourthaspect of the present invention, a reinforcement layer made of a hardermaterial than the material of which the thermal insulation area is madeis provided on at least one face orthogonal to a thickness direction ofthe thermal insulation area. The joint strength of the semiconductorsubstrate and the flexible area can be increased.

In a sixth aspect of the present invention, in the fifth aspect of thepresent invention, the reinforcement layer has a Young's modulus of9.8×10⁹ N/m² or more. The joint strength of the semiconductor substrateand the flexible area can be increased.

In a seventh aspect of the present invention, in the sixth aspect of thepresent invention, the reinforcement layer is a silicon dioxide thinfilm. The joint strength of the semiconductor substrate and the flexiblearea can be increased.

In an eighth aspect of the present invention, in the first to seventhaspect of the present invention, the portions of the semiconductorsubstrate and the flexible area in contact with the thermal insulationarea form comb teeth. The joint strength of the semiconductor substrateand the flexible area can be increased.

According to a ninth aspect of the present invention, there is provideda semiconductor device comprising a semiconductor device as the first toeighth aspect of the present invention and a moving element placedcontiguous with the flexible area, wherein when temperature of theflexible area changes, the moving element is displaced relative to thesemiconductor substrate. The semiconductor device which has similaradvantages to those in the invention as claimed in claims 1 to 8 as wellas can be driven with low power consumption can be provided.

In a tenth aspect of the present invention, in the ninth aspect of thepresent invention, the flexible area has a cantilever structure. Thesemiconductor device can be provided with large displacement of themoving element.

In an eleventh aspect of the present invention, in ninth aspect of thepresent invention, the moving element is supported by a plurality offlexible areas. The moving element can be supported stably.

In a twelfth aspect of the present invention, in the eleventh aspect ofthe present invention, the flexible areas are in the shape of a crosswith the moving element at the center. Good displacement accuracy of themoving element can be provided.

In a thirteenth aspect of the present invention, in the ninth aspect ofthe present invention, displacement of the moving element containsdisplacement rotating in a horizontal direction to a substrate face ofthe semiconductor substrate. The displacement of the moving elementbecomes large.

In a fourteenth aspect of the present invention, in the eleventh orthirteenth aspect of the present invention, the flexible areas are fourflexible areas each shaped like L, the four flexible areas being placedat equal intervals in every direction with the moving element at thecenter. The lengths of the flexible areas can be increased, so that thedisplacement of the moving element can be made large.

In a fifteenth aspect of the present invention, in the ninth tofourteenth aspect of the present invention, the flexible area is made upof at least two areas having different thermal expansion coefficientsand is displaced in response to the difference between the thermalexpansion coefficients. As the temperature of the flexible area ischanged, the flexible area can be displaced.

In a sixteenth aspect of the present invention, in the fifteenth aspectof the present invention, the flexible area includes an area made ofsilicon and an area made of aluminum. As the temperature of the flexiblearea is changed, the flexible area can be displaced because of thethermal expansion difference between aluminum and silicon.

In a seventeenth aspect of the present invention, in the fifteenthaspect of the present invention, the flexible area includes an area madeof silicon and an area made of nickel. As the temperature of theflexible area is changed, the flexible area can be displaced because ofthe thermal expansion difference between nickel and silicon.

In a eighteenth aspect of the present invention, in the fifteenth aspectof the present invention, at least one of the areas making up theflexible area is made of the same material as the thermal insulationarea. Since the flexible area and the thermal insulation area can beformed at the same time, the manufacturing process is simplified and thecosts can be reduced.

In a nineteenth aspect of the present invention, in the eighteenthaspect of the present invention, the flexible area includes an area madeof silicon and an area made of polyimide as the area made of the samematerial as the thermal insulation area. In addition to a similaradvantage to that in the invention, as the temperature of the flexiblearea is changed, the flexible area can be displaced because of thethermal expansion difference between silicon and polyimide, and the heatinsulation properties of the flexible area owing to polyimide.

In a twentieth aspect of the present invention the invention, in theeighteenth aspect of the present invention, the flexible area includesan area made of silicon and an area made of a fluoridated resin as thearea made of the same material as the thermal insulation area. Inaddition to a similar advantage, as the temperature of the flexible areais changed, the flexible area can be displaced because of the thermalexpansion difference between silicon and the fluoridated resin, and theheat insulation properties of the flexible area owing to the fluoridatedresin.

In a twenty-first aspect of the present invention, in the ninth tofourteenth aspect of the present invention, the flexible area is made ofa shape memory alloy. As the temperature of the flexible area ischanged, the flexible area can be displaced.

In a twenty-second aspect of the present invention, in the ninth totwenty-first aspect of the present invention, a thermal insulation areamade of a resin for joining the flexible area and the moving element isprovided between the flexible area and the moving element. The heatinsulation properties between the flexible area and the moving elementcan be provided and power consumption when the temperature of theflexible area is changed can be more suppressed.

In a twenty-third aspect of the present invention, in the twenty-secondaspect of the present invention, wherein rigidity of the thermalinsulation area provided between the semiconductor substrate and theflexible area is made different from that of the thermal insulation areaprovided between the flexible area and the moving element. Thedisplacement direction of the moving element can be determined dependingon the rigidity difference between the thermal insulation areas.

In a twenty-fourth aspect of the present invention, in the ninth totwenty-third aspects of the present invention, the flexible areacontains heat means for heating the flexible area. The semiconductordevice can be miniaturized.

In a twenty-fifth aspect of the present invention, in the ninth totwenty-fifth aspects of the present invention, wiring for supplyingpower to the heat means for heating the flexible area is formed withoutthe intervention of the thermal insulation area. The heat insulationdistance of the wiring can be increased and the heat insulationproperties of the flexible area can be enhanced.

In a twenty-sixth aspect of the present invention, in the ninth totwenty-fifth aspect of the present invention, the moving element isformed with a concave part. The heat capacity of the moving element islessened, so that the temperature change of the flexible area can beaccelerated.

In a twenty-seventh aspect of the present invention, in the ninth totwenty-sixth aspects of the present invention, a round for easing astress is provided in the proximity of the joint part of the flexiblearea and the moving element or the semiconductor substrate. The stressapplied in the proximity of the joint part when the flexible area isdisplaced is spread by means of the round, whereby the part can beprevented from being destroyed.

In a twenty-eighth aspect of the present invention, in thetwenty-seventh aspect of the present invention, the semiconductorsubstrate is formed with a projection part projecting toward the jointpart to the flexible area and the round is formed so that the shape ofthe round on the substrate face on the semiconductor substrate becomeslike R at both ends of the base end part of the projection part. Thestress applied to both ends of the base end part of the projection partwhen the flexible area is displaced is spread by means of the round,whereby the portion can be prevented from being destroyed.

In a twenty-ninth aspect of the present invention, in twenty-seventhaspect of the present invention, the semiconductor substrate is etchedfrom the substrate face to make a concave part, the flexible area isformed in a bottom face part of the concave part, and the round isformed so as to become shaped like R on the boundary between the bottomface part and a flank part of the concave part. The stress applied tothe boundary between the bottom face part and the flank part of theconcave part when the flexible area is displaced is spread by means ofthe round, whereby the portion can be prevented from being destroyed.

According to a thirtieth aspect of the present invention, there isprovided a semiconductor microvalve comprising a semiconductor device inany of ninth to twenty-ninth aspects and a fluid element being joined tothe semiconductor device and having a flow passage with a flowing fluidquantity changing in response to displacement of the moving element. Thesemiconductor microvalve which has similar advantages in ninth totwenty-ninth aspect of the present invention as well as can be drivenwith low power consumption can be provided.

In a thirty-first aspect of the present invention, in the thirties ofthe present invention, the semiconductor device and the fluid elementare joined by anodic junction. It is made possible to join thesemiconductor device and the fluid element.

In a thirty-second aspect of the present invention, in the thirtiesaspect of the present invention, the semiconductor device and the fluidelement are joined by eutectic junction. It is made possible to join thesemiconductor device and the fluid element.

In a thirty-third aspect of the present invention, in the thirtiethaspect of the present invention, the semiconductor device and the fluidelement are joined via a spacer layer. The thermal expansion differencebetween the semiconductor device and the fluid element when they arejoined is absorbed in the spacer layer and the stress applied to theflexible area can be suppressed.

In a thirty-fourth aspect of the present invention, in the thirty-thirdaspect of the present invention, the spacer layer is made of polyimide.The thermal expansion difference between the semiconductor device andthe fluid element when they are joined is absorbed because of elasticityof polyimide and the stress applied to the flexible area can besuppressed.

According to a thirty-fifth aspect of the present invention, there isprovided a semiconductor microrelay comprising a semiconductor device asthe ninth to twenty ninth aspect of the present invention and a fixedelement being joined to the semiconductor device and having fixedcontacts being placed at positions corresponding to a moving contactprovided on the moving element, the fixed contacts being able to come incontact with the moving contact. The semiconductor microrelay which hassimilar advantages to those in the invention as claimed in claims 9 to29 as well as can be driven with low power consumption can be provided.

In a thirty-sixth aspect of the present invention, in the thirty-fifthaspect of the present invention, the fixed contacts are placed away fromeach other and come in contact with the moving contact, whereby they arebrought into conduction via the moving contact. The semiconductormicrorelay wherein the fixed contacts placed away from each other can bebrought into conduction can be provided.

In a thirty-seventh aspect of the present invention, in the thirty-fifthor thirty-sixth aspect of the present invention, the moving contact andthe fixed contacts are gold cobalt. The moving contact and the fixedcontacts can be brought into conduction.

In a thirty-eighth aspect of the present invention, in the thirty-fifthto thirty-seventh aspect of the present invention, the semiconductordevice and the fixed element are joined by anodic junction. It is madepossible to join the semiconductor device and the fixed element.

In a thirty-ninth aspect of the present invention, in the thirty-fifthto thirty-seventh aspect of the present invention, the semiconductordevice and the fixed element are joined by eutectic junction. It is madepossible to join the semiconductor device and the fixed element.

In a fortieth aspect of the present invention, in the thirty-fifth tothirty-seventh aspect of the present invention, the semiconductor deviceand the fixed element are joined via a spacer layer. The thermalexpansion difference between the semiconductor device and the fluidelement when they are joined is absorbed in the spacer layer and thestress applied to the flexible area can be suppressed.

In a forty-first aspect of the present invention, in the fortieth aspectof the present invention, the spacer layer is made of polyimide. Thethermal expansion difference between the semiconductor device and thefluid element when they are joined is absorbed because of elasticity ofpolyimide and the stress applied to the flexible area can be suppressed.

According to a forty-second aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in theeighteenth aspect of the present invention prepared by a processcomprising the steps of:

etching and removing one face of the semiconductor substrate to form abottom face part as one area forming a part of the flexible area;

etching and removing the other face of the semiconductor substrate toform the concave part in the moving element;

etching and removing the other face of the semiconductor substrate toform at least a portion which becomes the thermal insulation area placedbetween the semiconductor substrate and the flexible area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

applying a coat of the thermal insulation material to the one face ofthe semiconductor substrate to form one area forming a part of theflexible area.

The thermal insulation area and one area forming a part of the flexiblearea are formed of the same material at the same time, whereby themanufacturing process is simplified and the costs can be reduced.

According to a forty-third aspect of the present invention, there isprovided a manufacturing method of a semiconductor device area;

etching and removing the other face of the semiconductor substrate toform the concave part in the moving element;

etching and removing the other face of the semiconductor substrate toform at least a portion which becomes the thermal insulation area placedbetween the semiconductor substrate and the flexible area;

forming a wire for applying an electric power to the heating means;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

forming a nickel thin film as an area defined in the flexible area onthe other face of the semiconductor substrate, whereby the area definedby nickel could be formed in the flexible area.

According to a forty-fifth aspect of the present invention there isprovided a manufacturing method of a semiconductor device in the firstaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form atleast a portion which becomes the thermal insulation area placed betweenthe semiconductor substrate and the flexible area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

etching and removing the other face of the semiconductor substrate toform the thermal insulation area, whereby the thermal isolation areacould be placed between the semiconductor substrate and the flexiblearea.

According to a forty-sixth aspect of the present invention, there isprovided a manufacturing method of a semiconductor device in the fifthaspect of the present invention prepared by a process comprising thesteps of:

etching and removing one face of the semiconductor substrate to form atleast a portion which becomes the thermal insulation area placed betweenthe semiconductor substrate and the flexible area;

forming a reinforce layer in the thermal insulation area;

filling the portion which becomes the thermal insulation area with athermal insulation material to form the thermal insulation area; and

etching and removing the other face of the semiconductor substrate toform the thermal insulation area, whereby the thermal isolation areacould be placed between the semiconductor substrate and the flexiblearea and the reinforce layer could be formed in the thermal insulationarea.

What is claimed is:
 1. A semiconductor microvalve comprising: asemiconductor substrate; a flexible member isolated from saidsemiconductor substrate and displaced in response to temperature change;a thermal isolation member placed between said semiconductor substrateand said flexible member and made of a resin for joining saidsemiconductor substrate and said flexible member; and a moving elementplaced contiguous with the flexible member, said moving element beingdisplaced relative to the semiconductor substrate when temperature ofthe flexible member changes; a fluid element being joined to saidsemiconductor device and having a flow passage with a flowing fluidquantity changing in response to displacement of the moving element, andwherein portions of said semiconductor substrate and said flexiblemember in contact with said thermal isolation member form comb teeth. 2.The semiconductor microvalve as claimed in claim 1, wherein saidsemiconductor device and said fluid element are joined via a spacerlayer.
 3. The semiconductor device as claimed in claim 1, wherein thematerial of which said thermal isolation member is made has a thermalconductivity coefficient of about 0.4 W/(m° C.) or less.
 4. Thesemiconductor device as claimed in claim 1, wherein the material ofwhich said thermal isolation member is made is polyimide.
 5. Thesemiconductor device as claimed in claim 1, wherein the material ofwhich said thermal isolation member is made is a fluoridated resin. 6.The semiconductor device as claimed in claim 1, wherein a reinforcementlayer made of a harder material than the material of which said thermalisolation member is made is provided on at least one face orthogonal toa thickness direction of said thermal isolation member.
 7. Thesemiconductor device as claimed in claim 6, wherein the reinforcementlayer has a Young's modulus of 9.8×10⁹ N/m² or more.
 8. Thesemiconductor device as claimed in claim 6, wherein the reinforcementlayer is a silicon dioxide thin film.
 9. The semiconductor device asclaimed in claim 1, wherein the flexible member has a cantileverstructure.
 10. The semiconductor device as claimed in claim 1, whereinsaid moving element is supported by a plurality of flexible members. 11.The semiconductor device as claimed in claim 10, wherein the flexiblemembers are in the shape of a cross with said moving element at thecenter.
 12. The semiconductor device as claimed in claim 10, whereindisplacement of said moving element includes displacement rotating in ahorizontal direction to a substrate face of the semiconductor substrate.13. The semiconductor device as claimed in claim 10, wherein theflexible members are four flexible members each shaped in L, the fourflexible members being placed at equal intervals in every direction withsaid moving element at the center.
 14. The semiconductor device asclaimed in claim 1, wherein the flexible member is made up of at leasttwo members having different thermal expansion coefficients and isdisplaced in response to a difference between the thermal expansioncoeffficients.
 15. The semiconductor device as claimed in claim 14,wherein the flexible member includes an member made of silicon and anmember made of aluminum.
 16. The semiconductor device as claimed inclaim 14, wherein the flexible member includes an member made of siliconand an member made of nickel.
 17. The semiconductor device as claimed inclaim 14, wherein at least one of the members making up the flexiblemember is made of the same material as the thermal isolation member. 18.The semiconductor device as claimed in claim 17, wherein the flexiblemember includes an member made of silicon and an member made ofpolyimide as the member made of the same material as the thermalisolation member.
 19. The semiconductor device as claimed in claim 17,wherein the flexible member includes an member made of silicon and anmember made of a fluoridated resin as the member made of the samematerial as the thermal isolation member.
 20. The semiconductor deviceas claimed in claim 1, wherein the flexible member is made of a shapememory alloy.
 21. The semiconductor device as claimed in claim 1,wherein a thermal isolation member made of a resin for joining theflexible member and said moving element is provided between the flexiblemember and said moving element.
 22. The semiconductor device as claimedin claim 21, wherein rigidity of the thermal isolation member providedbetween the semiconductor substrate and the flexible member is madedifferent form that of the thermal isolation member provided between theflexible member and said moving element.
 23. The semiconductor device asclaimed in claim 1, wherein the flexible member contains a heater forheating the flexible member.
 24. The semiconductor device as claimed inclaim 23 further comprising: wiring for supplying power to the heaterfor heating the flexible member is formed without the intervention ofthe thermal isolation member.